Loop parallelization analyzer for data flow programs

ABSTRACT

System and method for automatically parallelizing iterative functionality in a data flow program. A data flow program is stored that includes a first data flow program portion, where the first data flow program portion is iterative. Program code implementing a plurality of second data flow program portions is automatically generated based on the first data flow program portion, where each of the second data flow program portions is configured to execute a respective one or more iterations. The plurality of second data flow program portions are configured to execute at least a portion of iterations concurrently during execution of the data flow program. Execution of the plurality of second data flow program portions is functionally equivalent to sequential execution of the iterations of the first data flow program portion.

FIELD OF THE INVENTION

The present invention relates to the field of data flow programming, andmore particularly to automatically parallelizing iterative functionalityin data flow programs.

DESCRIPTION OF THE RELATED ART

Data flow programming is a programming approach or protocol with manyindustrial (and other) applications. In data flow (or dataflow)programming, the program architecture is that of a directed graphspecifying the flow of data through the program. In data flow programsfunctions execute whenever the necessary input data are available. Dataflow programs can be contrasted with procedural programs, which specifyan execution flow of computations to be performed.

Graphical programming has also become a powerful tool available toprogrammers. Graphical programming environments such as the NationalInstruments LabVIEW product have become very popular. Tools such asLabVIEW have greatly increased the productivity of programmers, andincreasing numbers of programmers are using graphical programmingenvironments to develop their software applications. In particular,graphical programming tools are being used for test and measurement,data acquisition, process control, man machine interface (MMI),supervisory control and data acquisition (SCADA) applications, modeling,simulation, image processing/machine vision applications, and motioncontrol, among others.

Graphical data flow programs or diagrams, such as LabVIEW, combine theabove two paradigms. A graphical program or diagram includes a pluralityof interconnected nodes (or blocks), where at least a subset of theconnections among the nodes visually indicate that data produced by onenode is used by another node. A LabVIEW VI is one example of a graphicaldata flow program; a Simulink block diagram is another example of agraphical data flow program.

Increasingly, computer systems include multiprocessing capabilities,e.g., computers with multiple processors, processors with multipleprocessing cores, networked computers, etc., that may be used to executeprograms in a parallel manner, i.e., concurrently. However, implementingsuch parallelism in current graphical programming systems requires thata user analyze the graphical program code, the execution target(multi-core/multi-processor), and the data to be processed, and manuallycustomize the graphical program, e.g., writing or rewriting graphicalprogram code, which may be difficult, tedious, and error prone. Forexample, LabVIEW's dataflow layout naturally separates independentoperations so that they may be efficiently executed in separate threadson a multi-core system. FOR loops, however, are currently treated asexplicitly sequential. Users frequently place repetitive operations in aloop structure for easier expressibility, even if the operations do notneed to be executed in a sequential order. Currently, if a user desiresbetter multi-core performance from code that uses loops, the user mustexplicitly split the inputs and FOR loop operations into multiple copiesof the operations to execute the code in parallel. There is no way toeasily tune or test such transformations by hand.

Thus, improved systems and methods for parallelizing data flow programfunctionality are desired.

SUMMARY OF THE INVENTION

Various embodiments of a system and method for enabling a graphicalprogram to automatically parallelize iterative graphical program codeare presented below.

A data flow program may be stored, e.g., in a memory medium, where thedata flow program has a first data flow program portion, and where thefirst data flow program portion is iterative. In other words, the firstdata flow program portion comprises an iterative processing structure orcode that specifies or implements iterative execution of data flowprogram code. Note that in various embodiments, the data flow programmay be a text-based data flow program, or may be a graphical data flowprogram. For example, in one embodiment, the first graphical data flowprogram portion may be or include a loop graphical program structure.

For example, in one embodiment, the data flow program is a graphicaldata flow program that may be displayed on a display device, e.g., acomputer monitor of a computer system, and that includes a plurality ofinterconnected nodes that visually indicate functionality of thegraphical data flow program. The graphical data flow program thus has afirst graphical data flow program portion, where the first graphicaldata flow program portion is iterative. For example, the first graphicaldata flow program portion may be or include a loop graphical programstructure.

In graphical data flow program embodiments, the first graphical dataflow program portion, e.g., the graphical program loop structurepreferably includes an interior, and is configured to iterativelyexecute graphical program code comprised in the interior. In someembodiments, the first graphical data flow program portion, e.g., thegraphical program loop structure, may be a graphical program node, e.g.,a graphical loop node. For example, the node may include an icon with aloop border that encloses the interior (and any graphical program codecontained therein). The loop border, which may be referred to simply asthe “loop”, along with its contained code, may be referred to as thebody of the loop node or structure. In preferred embodiments, the firstgraphical data flow program portion may be or include a FOR loop, andthe node may be a FOR loop node, although other types of paralleliterative processing nodes are also contemplated. For example, in caseswhere the loop is a “while loop”, but where the total number ofiterations to be performed may be determined prior to runtime, the whileloop may be automatically converted to a FOR loop node, according toembodiments described herein.

Moreover, in some embodiments, the FOR loop may be a parallel FOR loop,which denotes a FOR loop that is either marked for (attempted) automaticparallelization, or in some embodiments, that has already beenparallelized. Similarly, the graphical FOR loop may be or include aparallel graphical FOR loop, e.g., a parallel graphical program loopstructure. In some embodiments, a parallel FOR loop may includeadditional elements, structures, or configuration/interfacefunctionality, e.g., border nodes, as described below.

For example, in some embodiments, the graphical data flow program mayinclude a graphical indicator that specifies to a compiler that thecompiler is to attempt to automatically generate data flow program codethat parallelizes a specified portion of the graphical data flow programfor concurrent execution, e.g., the first portion of the graphical dataflow program. In some embodiments, the graphical indicator may be usedby the developer to specify such parallelization. Further detailsregarding embodiments of the graphical indicator are presented below.

The data flow program may be deployable to a target execution platformwith concurrent processing capabilities. For example, the targetexecution platform may include one or more of: one or more multi-coreprocessors, one or more hardware multi-threaded processors, one or moremulti-processor computers, or two or more networked computers.

The data flow program may automatically be analyzed. As noted above, itis important that there be no dependences between iterations, i.e., thatthe iterations may be performed independently of one another. Thus, insome embodiments, automatically analyzing the data flow program mayinclude automatically performing dependence analysis of the first dataflow program portion. Dependence analysis refers to analysis ofdependences (or dependencies) between program elements, includingdependences between iterations of iterative program code. In oneembodiment, dependence analysis and reduction operation analysis of thedata flow program may be automatically performed, e.g., via softwareexecuting on the computer system, i.e., programmatically. Reductionoperation analysis refers to analysis regarding operations that collectand combine or merge results from separate processes, e.g., concurrentprocesses, program portions, etc., to generate reduced or mergedresults, and may include dependence analysis regarding the reductionoperations. However, it should be noted that reduction operationanalysis may involve more than just data/order dependence analysis. Itmay also require interpreting operations performed by particular programelements, e.g., data flow nodes, to determine if they are reductionoperations, and to infer or otherwise determine the appropriateinitialization values for particular reduction operations.

Performing dependence analysis and reduction operation analysis of thedata flow program may include determining that the first data flowprogram portion cannot be parallelized as specified, and indicating oneor more errors preventing parallelization or one or more warningsregarding parallelization. In one embodiment, indicating the one or moreerrors may include indicating data flow program code that caused thedetermined errors or warnings. For example, the data flow program codethat caused the errors or warnings may be indicated by providinglocation or address information specifying the offending code, or theoffending data flow program code may itself be displayed, among otherindication means.

Program code implementing a plurality of second data flow programportions may be generated, e.g., automatically generated, based on thefirst data flow program portion, where each of the second data flowprogram portions is configured to execute a respective one or moreiterations. In one embodiment, the program code implementing a pluralityof second data flow program portions may be generated based on the firstdata flow program portion and the analysis (or analyses) describedabove. Note that as used herein, “automatic” means that the action isperformed by software, i.e., programmatically, and thus does not requiredirect user involvement, although the action may (or may not) be invokedor configured by the user. In graphical data flow embodiments where thegraphical data flow program includes a graphical indicator specifyingthat parallelization is to be attempted, the automatic generation ofprogram code implementing the plurality of second data flow programportions may be performed based on the graphical indicator.

The plurality of second data flow program portions may be configured toexecute at least a portion of iterations concurrently during executionof the data flow program. Moreover, execution of the plurality of seconddata flow program portions may be functionally equivalent to sequentialexecution of the iterations of the first (possibly graphical) data flowprogram portion. In other words, the cumulative results of executing theplurality of second data flow program portions may be the same asresults that would have been produced by sequential iterative executionof the first data flow portion. Note that as used herein, “concurrently”means that at least a portion of the concurrent processes overlap intime, i.e., at least one of the instances must execute at least oneiteration while another instance executes another iteration.

The method may further include executing the data flow program,including each of the second data flow program portions executing therespective one or more iterations, where the plurality of second dataflow program portions collectively execute all iterations specified forthe first data flow program portion.

Note that the program code implementing the plurality of second dataflow program portions may be automatically generated in response tothere being no detected conditions preventing parallelization of thefirst data flow program portion. In other words, the program code may beautomatically generated contingent upon the parallelization beingfeasible, i.e., reliably implementable. The absence of such conditions(preventing parallelization) may be determined via analysis of the dataflow program, as described in more detail herein.

In various embodiments, any of the techniques and functionalitiesdisclosed herein may be implemented as part of a developmentenvironment. However, in some embodiments, the above analyses (and anyother functionalities disclosed herein) may be performed by a separatetool, e.g., a standalone software program or tool, that may be used orinvoked by or from within a development environment, or independent fromsuch an environment. For example, in one embodiment, the tool may beprovided by, or even executed on, a server. In one embodiment, thetool's functionality may be implemented as an API (applicationprogramming interface), which may be utilized or otherwise invoked orcalled by a GUI, e.g., of the separate tool, or, in other embodiments,of the development environment, or even another program. More generally,while in some embodiments, the tool may be specifically directed toanalyzing data flow programs to determine whether they can beparallelized, in various embodiments, the tool may be further executableto perform any of the various techniques and functionalities disclosedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1A illustrates a computer system configured to execute a graphicalprogram according to an embodiment of the present invention;

FIG. 1B illustrates a network system comprising two or more computersystems that may implement an embodiment of the present invention;

FIG. 2A illustrates an instrumentation control system according to oneembodiment of the invention;

FIG. 2B illustrates an industrial automation system according to oneembodiment of the invention;

FIG. 3A is a high level block diagram of an exemplary system which mayexecute or utilize graphical programs;

FIG. 3B illustrates an exemplary system which may perform control and/orsimulation functions utilizing graphical programs;

FIG. 4 is an exemplary block diagram of the computer systems of FIGS.1A, 1B, 2A and 2B and 3B;

FIG. 5 illustrates a multi-core computer system, according to oneembodiment;

FIG. 6A-6B illustrate manual parallelization of a graphical loopstructure, according to the prior art;

FIG. 7 is a flowchart diagram illustrating one embodiment of a methodfor automatically parallelizing data flow program code;

FIGS. 8A and 8B illustrate exemplary embodiments of border nodes;

FIG. 9 illustrates an exemplary graphical program for matrixmultiplication that includes three nested FOR loops, according to oneembodiment;

FIG. 10 illustrates an exemplary parallelizeable loop, according to oneembodiment;

FIG. 11 illustrates an exemplary non-parallelizeable loop, according toone embodiment;

FIG. 12 illustrates exemplary constraints for solving an integer linearprogramming problem, according to one embodiment;

FIGS. 13A-13D illustrate array analysis of an LU decomposition diagram,according to one embodiment;

FIG. 14 illustrates exemplary partitioning of sixteen iterations amongfour processors when index blocksize is two, according to oneembodiment;

FIG. 15 illustrates an exemplary data flow program where computationalload is not balanced among iterations, according to one embodiment;

FIG. 16 illustrates output from an exemplary data flow program forcomputing the Mandelbrot set, according to one embodiment;

FIG. 17 illustrates performance differences between exemplary graphicalprograms for computing the Mandelbrot set according to variousscheduling strategies, according to one embodiment;

FIGS. 18A-18D illustrate use of an exemplary wrapper for implementingstatic allocation of workers, according to one embodiment;

FIGS. 19A and 19B illustrate an exemplary simple GUI for specifying ordetermining whether parallelism is to be considered for a graphicalprogram loop, according to one embodiment;

FIGS. 20A-20G illustrate exemplary graphical user interfaces (GUIs) forparallelizing iterative data flow programs, according to variousembodiments;

FIG. 21 illustrates a simple graphical parallel loop detection functionthat does not support errors or warnings, according to one embodiment;

FIG. 22 illustrates a more complex graphical parallel loop detectionfunction that supports errors and warnings, according to one embodiment;and

FIG. 23 illustrates exemplary output from the function of FIG. 22,according to one embodiment.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Incorporation by Reference:

The following references are hereby incorporated by reference in theirentirety as though fully and completely set forth herein:

U.S. Pat. No. 4,914,568 titled “Graphical System for Modeling a Processand Associated Method,” issued on Apr. 3, 1990.

U.S. Pat. No. 5,481,741 titled “Method and Apparatus for ProvidingAttribute Nodes in a Graphical Data Flow Environment”.

U.S. Pat. No. 6,173,438 titled “Embedded Graphical Programming System”filed Aug. 18, 1997.

U.S. Pat. No. 6,219,628 titled “System and Method for Configuring anInstrument to Perform Measurement Functions Utilizing Conversion ofGraphical Programs into Hardware Implementations,” filed Aug. 18, 1997.

U.S. Patent Application Publication No. 20010020291 (Ser. No.09/745,023) titled “System and Method for Programmatically Generating aGraphical Program in Response to Program Information,” filed Dec. 20,2000.

Terms

The following is a glossary of terms used in the present application:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks 104, or tape device; a computer systemmemory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM,Rambus RAM, etc.; or a non-volatile memory such as a magnetic media,e.g., a hard drive, or optical storage. The memory medium may compriseother types of memory as well, or combinations thereof. In addition, thememory medium may be located in a first computer in which the programsare executed, and/or may be located in a second different computer whichconnects to the first computer over a network, such as the Internet. Inthe latter instance, the second computer may provide programinstructions to the first computer for execution. The term “memorymedium” may include two or more memory mediums which may reside indifferent locations, e.g., in different computers that are connectedover a network.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Program—the term “program” is intended to have the full breadth of itsordinary meaning. The term “program” includes 1) a software programwhich may be stored in a memory and is executable by a processor or 2) ahardware configuration program useable for configuring a programmablehardware element.

Software Program—the term “software program” is intended to have thefull breadth of its ordinary meaning, and includes any type of programinstructions, code, script and/or data, or combinations thereof, thatmay be stored in a memory medium and executed by a processor. Exemplarysoftware programs include programs written in text-based programminglanguages, such as C, C++, PASCAL, FORTRAN, COBOL, JAVA, assemblylanguage, etc.; graphical programs (programs written in graphicalprogramming languages); assembly language programs; programs that havebeen compiled to machine language; scripts; and other types ofexecutable software. A software program may comprise two or moresoftware programs that interoperate in some manner. Note that variousembodiments described herein may be implemented by a computer orsoftware program. A software program may be stored as programinstructions on a memory medium.

Hardware Configuration Program—a program, e.g., a netlist or bit file,that can be used to program or configure a programmable hardwareelement.

Graphical Program—A program comprising a plurality of interconnectednodes or icons, wherein the plurality of interconnected nodes or iconsvisually indicate functionality of the program. Graphical function nodesmay also be referred to as blocks.

The following provides examples of various aspects of graphicalprograms. The following examples and discussion are not intended tolimit the above definition of graphical program, but rather provideexamples of what the term “graphical program” encompasses:

The nodes in a graphical program may be connected in one or more of adata flow, control flow, and/or execution flow format. The nodes mayalso be connected in a “signal flow” format, which is a subset of dataflow.

Exemplary graphical program development environments which may be usedto create graphical programs include LabVIEW®, DasyLab™, DiaDem™ andMatrixx/SystemBuild™ from National Instruments, Simulink® from theMathWorks, VEE™ from Agilent, WiT™ from Coreco, Vision Program Manager™from PPT Vision, SoftWIRE™ from Measurement Computing, Sanscript™ fromNorthwoods Software, Khoros™ from Khoral Research, SnapMaster™ from HEMData, VisSim™ from Visual Solutions, ObjectBench™ by SES (Scientific andEngineering Software), and VisiDAQ™ from Advantech, among others.

The term “graphical program” includes models or block diagrams createdin graphical modeling environments, wherein the model or block diagramcomprises interconnected blocks (i.e., nodes) or icons that visuallyindicate operation of the model or block diagram; exemplary graphicalmodeling environments include Simulink®, SystemBuild™, VisSim™,Hypersignal Block Diagram™, etc.

A graphical program may be represented in the memory of the computersystem as data structures and/or program instructions. The graphicalprogram, e.g., these data structures and/or program instructions, may becompiled or interpreted to produce machine language that accomplishesthe desired method or process as shown in the graphical program.

Input data to a graphical program may be received from any of varioussources, such as from a device, unit under test, a process beingmeasured or controlled, another computer program, a database, or from afile. Also, a user may input data to a graphical program or virtualinstrument using a graphical user interface, e.g., a front panel.

A graphical program may optionally have a GUI associated with thegraphical program. In this case, the plurality of interconnected blocksor nodes are often referred to as the block diagram portion of thegraphical program.

Node—In the context of a graphical program, an element that may beincluded in a graphical program. The graphical program nodes (or simplynodes) in a graphical program may also be referred to as blocks. A nodemay have an associated icon that represents the node in the graphicalprogram, as well as underlying code and/or data that implementsfunctionality of the node. Exemplary nodes (or blocks) include functionnodes, sub-program nodes, terminal nodes, structure nodes, etc. Nodesmay be connected together in a graphical program by connection icons orwires.

Graphical Data Flow Program (or Graphical Data Flow Diagram)—A graphicalprogram or diagram comprising a plurality of interconnected nodes(blocks), wherein at least a subset of the connections among the nodesvisually indicate that data produced by one node is used by anothernode. A LabVIEW VI is one example of a graphical data flow program. ASimulink block diagram is another example of a graphical data flowprogram.

Graphical User Interface—this term is intended to have the full breadthof its ordinary meaning. The term “Graphical User Interface” is oftenabbreviated to “GUI”. A GUI may comprise only one or more input GUIelements, only one or more output GUI elements, or both input and outputGUI elements.

The following provides examples of various aspects of GUIs. Thefollowing examples and discussion are not intended to limit the ordinarymeaning of GUI, but rather provide examples of what the term “graphicaluser interface” encompasses:

A GUI may comprise a single window having one or more GUI Elements, ormay comprise a plurality of individual GUI Elements (or individualwindows each having one or more GUI Elements), wherein the individualGUI Elements or windows may optionally be tiled together.

A GUI may be associated with a graphical program. In this instance,various mechanisms may be used to connect GUI Elements in the GUI withnodes in the graphical program. For example, when Input Controls andOutput Indicators are created in the GUI, corresponding nodes (e.g.,terminals) may be automatically created in the graphical program orblock diagram. Alternatively, the user can place terminal nodes in theblock diagram which may cause the display of corresponding GUI Elementsfront panel objects in the GUI, either at edit time or later at runtime. As another example, the GUI may comprise GUI Elements embedded inthe block diagram portion of the graphical program.

Front Panel—A Graphical User Interface that includes input controls andoutput indicators, and which enables a user to interactively control ormanipulate the input being provided to a program, and view output of theprogram, while the program is executing.

A front panel is a type of GUI. A front panel may be associated with agraphical program as described above.

In an instrumentation application, the front panel can be analogized tothe front panel of an instrument. In an industrial automationapplication the front panel can be analogized to the MMI (Man MachineInterface) of a device. The user may adjust the controls on the frontpanel to affect the input and view the output on the respectiveindicators.

Graphical User Interface Element—an element of a graphical userinterface, such as for providing input or displaying output. Exemplarygraphical user interface elements comprise input controls and outputindicators.

Input Control—a graphical user interface element for providing userinput to a program. An input control displays the value input the by theuser and is capable of being manipulated at the discretion of the user.Exemplary input controls comprise dials, knobs, sliders, input textboxes, etc.

Output Indicator—a graphical user interface element for displayingoutput from a program. Exemplary output indicators include charts,graphs, gauges, output text boxes, numeric displays, etc. An outputindicator is sometimes referred to as an “output control”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

Measurement Device—includes instruments, data acquisition devices, smartsensors, and any of various types of devices that are configured toacquire and/or store data. A measurement device may also optionally befurther configured to analyze or process the acquired or stored data.Examples of a measurement device include an instrument, such as atraditional stand-alone “box” instrument, a computer-based instrument(instrument on a card) or external instrument, a data acquisition card,a device external to a computer that operates similarly to a dataacquisition card, a smart sensor, one or more DAQ or measurement cardsor modules in a chassis, an image acquisition device, such as an imageacquisition (or machine vision) card (also called a video capture board)or smart camera, a motion control device, a robot having machine vision,and other similar types of devices. Exemplary “stand-alone” instrumentsinclude oscilloscopes, multimeters, signal analyzers, arbitrary waveformgenerators, spectroscopes, and similar measurement, test, or automationinstruments.

A measurement device may be further configured to perform controlfunctions, e.g., in response to analysis of the acquired or stored data.For example, the measurement device may send a control signal to anexternal system, such as a motion control system or to a sensor, inresponse to particular data. A measurement device may also be configuredto perform automation functions, i.e., may receive and analyze data, andissue automation control signals in response.

Subset—in a set having N elements, the term “subset” comprises anycombination of one or more of the elements, up to and including the fullset of N elements. For example, a subset of a plurality of icons may beany one icon of the plurality of the icons, any combination of one ormore of the icons, or all of the icons in the plurality of icons. Thus,a subset of an entity may refer to any single element of the entity aswell as any portion up to and including the entirety of the entity. Notethat a proper subset does not include the entirety of the entity.Moreover, disjoint subsets do not overlap in their membership.

Multiprocessor System—a computer system that includes multipleprocessing elements, i.e., processors, processing cores, or evennetworked computers, that may operate in a coordinated manner to executeprogram instructions concurrently.

FIG. 1A—Computer System

FIG. 1A illustrates a computer system 82 configured to implementembodiments of the present invention, i.e., configured with programinstructions according to embodiments of the invention. Morespecifically, the computer system 82 is configured to automaticallyparallelize graphical program code for concurrent execution by multipleprocessing elements, which may include multiple processors, processingcores, or even networked computers. Various embodiments of a method forparallelizing graphical program code in a graphical program aredescribed below.

As shown in FIG. 1A, the computer system 82 may include a display deviceconfigured to display the graphical program as the graphical program iscreated and/or executed. The display device may also be configured todisplay a graphical user interface or front panel of the graphicalprogram during execution of the graphical program. The graphical userinterface may comprise any type of graphical user interface, e.g.,depending on the computing platform.

The computer system 82 may include at least one memory medium on whichone or more computer programs or software components according to oneembodiment of the present invention may be stored. For example, thememory medium may store one or more graphical programs which areexecutable to perform the methods described herein. Additionally, thememory medium may store a graphical programming development environmentapplication used to create and/or execute such graphical programs. Insome embodiments, the graphical programming development environmentapplication may be configured to perform at least a portion of themethods described herein. The memory medium may also store operatingsystem software, as well as other software for operation of the computersystem. Various embodiments further include receiving or storinginstructions and/or data implemented in accordance with the foregoingdescription upon a carrier medium.

FIG. 1B—Computer Network

FIG. 1B illustrates a system including a first computer system 82 thatis coupled to a second computer system 90, where each of the computersystems is configured with program instructions according to embodimentsof the invention. The computer system 82 may be coupled via a network 84(or a computer bus) to the second computer system 90. The computersystems 82 and 90 may each be any of various types, as desired. Thenetwork 84 can also be any of various types, including a LAN (local areanetwork), WAN (wide area network), the Internet, or an Intranet, amongothers. The computer systems 82 and 90 may execute a graphical programin a distributed fashion. For example, computer 82 may execute a firstportion of the block diagram of a graphical program and computer system90 may execute a second portion of the block diagram of the graphicalprogram. As another example, computer 82 may display the graphical userinterface of a graphical program and computer system 90 may execute theblock diagram of the graphical program. In some embodiments, the twonetworked computers (and/or possibly others) may be a distributedexecution platform for parallelized graphical program code perembodiments of the present invention, as will be described in moredetail below.

In one embodiment, the graphical user interface of the graphical programmay be displayed on a display device of the computer system 82, and theblock diagram may execute on a device coupled to the computer system 82.The device may include a programmable hardware element and/or mayinclude a processor and memory medium which may execute a real timeoperating system. In one embodiment, the graphical program may bedownloaded and executed on the device. For example, an applicationdevelopment environment with which the graphical program is associatedmay provide support for downloading a graphical program for execution onthe device in a real time system.

Exemplary Systems

Embodiments of the present invention may be involved with performingtest and/or measurement functions; controlling and/or modelinginstrumentation or industrial automation hardware; modeling andsimulation functions, e.g., modeling or simulating a device or productbeing developed or tested, etc. Exemplary test applications where thegraphical program may be used include hardware-in-the-loop testing andrapid control prototyping, among others.

However, it is noted that the present invention can be used for aplethora of applications and is not limited to the above applications.In other words, applications discussed in the present description areexemplary only, and the present invention may be used in any of varioustypes of systems. Thus, the system and method of the present inventionis configured to be used in any of various types of applications,including the control of other types of devices such as multimediadevices, video devices, audio devices, telephony devices, Internetdevices, etc., as well as general purpose software applications such asword processing, spreadsheets, network control, network monitoring,financial applications, games, etc.

FIG. 2A illustrates an exemplary instrumentation control system 100which may implement embodiments of the invention. The system 100comprises a host computer 82 which couples to one or more instruments.The host computer 82 may comprise a central processing unit (CPU), adisplay screen, memory, and one or more input devices such as a mouse orkeyboard as shown. The computer 82 may operate with the one or moreinstruments to analyze, measure or control a unit under test (UUT) orprocess 150.

The one or more instruments may include a GPIB instrument 112 andassociated GPIB interface card 122, a data acquisition board 114inserted into or otherwise coupled with chassis 124 with associatedsignal conditioning circuitry 126, a VXI instrument 116, a PXIinstrument 118, a video device or camera 132 and associated imageacquisition (or machine vision) card 134, a motion control device 136and associated motion control interface card 138, and/or one or morecomputer based instrument cards 142, among other types of devices. Thecomputer system may couple to and operate with one or more of theseinstruments. The instruments may be coupled to the unit under test (UUT)or process 150, or may be coupled to receive field signals, typicallygenerated by transducers. The system 100 may be used in a dataacquisition and control application, in a test and measurementapplication, an image processing or machine vision application, aprocess control application, a man-machine interface application, asimulation application, or a hardware-in-the-loop validationapplication, among others.

FIG. 2B illustrates an exemplary industrial automation system 160 whichmay implement embodiments of the invention. The industrial automationsystem 160 is similar to the instrumentation or test and measurementsystem 100 shown in FIG. 2A. Elements which are similar or identical toelements in FIG. 2A have the same reference numerals for convenience.The system 160 may comprise a computer 82 which couples to one or moredevices or instruments. The computer 82 may comprise a CPU, a displayscreen, memory, and one or more input devices such as a mouse orkeyboard as shown. The computer 82 may operate with the one or moredevices to perform an automation function with respect to a process ordevice 150, such as MMI (Man Machine Interface), SCADA (SupervisoryControl and Data Acquisition), portable or distributed data acquisition,process control, advanced analysis, or other control, among others.

The one or more devices may include a data acquisition board 114inserted into or otherwise coupled with chassis 124 with associatedsignal conditioning circuitry 126, a PXI instrument 118, a video device132 and associated image acquisition card 134, a motion control device136 and associated motion control interface card 138, a fieldbus device170 and associated fieldbus interface card 172, a PLC (ProgrammableLogic Controller) 176, a serial instrument 182 and associated serialinterface card 184, or a distributed data acquisition system, such asthe Fieldpoint system available from National Instruments, among othertypes of devices.

FIG. 3A is a high level block diagram of an exemplary system which mayexecute or utilize graphical programs. FIG. 3A illustrates a generalhigh-level block diagram of a generic control and/or simulation systemwhich comprises a controller 92 and a plant 94. The controller 92represents a control system/algorithm the user may be trying to develop.The plant 94 represents the system the user may be trying to control.For example, if the user is designing an ECU for a car, the controller92 is the ECU and the plant 94 is the car's engine (and possibly othercomponents such as transmission, brakes, and so on.) As shown, a usermay create a graphical program that specifies or implements thefunctionality of one or both of the controller 92 and the plant 94. Forexample, a control engineer may use a modeling and simulation tool tocreate a model (graphical program) of the plant 94 and/or to create thealgorithm (graphical program) for the controller 92.

FIG. 3B illustrates an exemplary system which may perform control and/orsimulation functions. As shown, the controller 92 may be implemented bya computer system 82 or other device (e.g., including a processor andmemory medium and/or including a programmable hardware element) thatexecutes or implements a graphical program. In a similar manner, theplant 94 may be implemented by a computer system or other device 144(e.g., including a processor and memory medium and/or including aprogrammable hardware element) that executes or implements a graphicalprogram, or may be implemented in or as a real physical system, e.g., acar engine.

In one embodiment of the invention, one or more graphical programs maybe created which are used in performing rapid control prototyping. RapidControl Prototyping (RCP) generally refers to the process by which auser develops a control algorithm and quickly executes that algorithm ona target controller connected to a real system. The user may develop thecontrol algorithm using a graphical program, and the graphical programmay execute on the controller 92, e.g., on a computer system or otherdevice. The computer system 82 may be a platform that supports real timeexecution, e.g., a device including a processor that executes a realtime operating system (RTOS), or a device including a programmablehardware element.

In one embodiment of the invention, one or more graphical programs maybe created which are used in performing Hardware in the Loop (HIL)simulation. Hardware in the Loop (HIL) refers to the execution of theplant model 94 in real time to test operation of a real controller 92.For example, once the controller 92 has been designed, it may beexpensive and complicated to actually test the controller 92 thoroughlyin a real plant, e.g., a real car. Thus, the plant model (implemented bya graphical program) is executed in real time to make the realcontroller 92 “believe” or operate as if it is connected to a realplant, e.g., a real engine.

In the embodiments of FIGS. 2A, 2B, and 3B above, one or more of thevarious devices may couple to each other over a network, such as theInternet. In one embodiment, the user operates to select a target devicefrom a plurality of possible target devices for programming orconfiguration using a graphical program. Thus the user may create agraphical program on a computer and use (execute) the graphical programon that computer or deploy the graphical program to a target device (forremote execution on the target device) that is remotely located from thecomputer and coupled to the computer through a network.

Graphical software programs which perform data acquisition, analysisand/or presentation, e.g., for measurement, instrumentation control,industrial automation, modeling, or simulation, such as in theapplications shown in FIGS. 2A and 2B, may be referred to as virtualinstruments.

FIG. 4—Computer System Block Diagram

FIG. 4 is a block diagram representing one embodiment of the computersystem 82 and/or 90 illustrated in FIGS. 1A and 1B, or computer system82 shown in FIG. 2A or 2B. It is noted that any type of computer systemconfiguration or architecture can be used as desired, and FIG. 4illustrates a representative PC embodiment. It is also noted that thecomputer system may be a general purpose computer system, a computerimplemented on a card installed in a chassis, or other types ofembodiments. Elements of a computer not necessary to understand thepresent description have been omitted for simplicity.

The computer may include at least one central processing unit or CPU(processor) 160 which is coupled to a processor or host bus 162. The CPU160 may be any of various types, including an x86 processor, e.g., aPentium class, a PowerPC processor, a CPU from the SPARC family of RISCprocessors, as well as others. In some embodiments, the CPU 160 may be amulti-core processor that includes a plurality of processing cores forconcurrent execution of program instructions. A memory medium, typicallycomprising RAM and referred to as main memory, 166 is coupled to thehost bus 162 by means of memory controller 164. The main memory 166 maystore program instructions implementing embodiments of the presentinvention, including, for example, a graphical program developmentenvironment and one or more graphical programs. The main memory may alsostore operating system software, as well as other software for operationof the computer system.

The host bus 162 may be coupled to an expansion or input/output bus 170by means of a bus controller 168 or bus bridge logic. The expansion bus170 may be the PCI (Peripheral Component Interconnect) expansion bus,although other bus types can be used. The expansion bus 170 includesslots for various devices such as described above. The computer 82further comprises a video display subsystem 180 and hard drive 182coupled to the expansion bus 170.

As shown, a device 190 may also be connected to the computer. The device190 may include a processor and memory which may execute a real timeoperating system. The device 190 may also or instead comprise aprogrammable hardware element. The computer system may be configured todeploy a graphical program to the device 190 for execution of thegraphical program on the device 190. The deployed graphical program maytake the form of graphical program instructions or data structures thatdirectly represents the graphical program. Alternatively, the deployedgraphical program may take the form of text code (e.g., C code)generated from the graphical program. As another example, the deployedgraphical program may take the form of compiled code generated fromeither the graphical program or from text code that in turn wasgenerated from the graphical program.

FIG. 5—Multi-Core System

FIG. 5 illustrates a multi-core processing system, according to oneexemplary embodiment. As may be seen, in this embodiment, the multi-coreprocessing system is a multi-core processor (e.g., a multi-core CPU)160A with four processing cores 502, 504, 506, and 508, and memory cache540, all coupled together via a bus 520. Note that while in theembodiment shown a single cache is shared by all the processing cores,in other embodiments, one or more, or each, of the cores may have itsown cache, or groups of the cores may share respective caches, and soforth, as desired.

While the multi-core processing system shown in FIG. 5 is an exemplarytarget execution platform for embodiments of the present invention, itshould be noted that other platforms are also contemplated. For example,in various embodiments, the target execution platform may be or includeone or more multi-core processors, one or more multi-processorcomputers, and/or two or more networked computers. In other words, thetarget platform maybe any kind of computing system that includesmultiple processing elements, be they processing cores, processors, oreven networked processing devices.

Overview of Loop Parallelization

As indicated above, parallelization of iterative program code canprovide numerous performance benefits over serially iterative programcode.

FIG. 6A illustrates an exemplary graphical data flow program thatincludes a graphical iterative structure, e.g., a graphical FOR loop610, used to implement a matrix multiplication. Note that in theembodiment shown, the graphical FOR loop 610 has a boundary or borderthat forms or demarcates an interior portion within which graphical dataflow code may be placed, i.e., one or more graphical program nodes to beexecuted iteratively may be included within the interior of thestructure, where the graphical FOR loop specifies iterative execution ofthis contained graphical program code. Note further that in thisexample, the FOR loop 610 contains two further FOR loops, i.e., nestedFOR loops, although for brevity only the outer loop 610 is consideredherein.

In prior art approaches to parallelization of such a FOR loop, e.g., byimplementing M, e.g., 2 or 4, concurrent looping structures, thedeveloper would have to do their own analysis to determine ifparallelization is safe and reliable, then copy the loop M (e.g., 2 or4) times and modify the surrounding code, which is labor intensive andprone to error.

FIG. 6B illustrates an exemplary graphical data flow program thatimplements parallelization of the graphical program of FIG. 6A by(manually) constructing two concurrent loops 620 and 630, where eachconcurrent loop operates to perform a respective portion of theiterations specified for the original loop 610. Such manualparallelization of loop 610 requires significant effort. Moreover,subsequent to the (manual) parallelization, there may be a requirementto scale the parallelization up to 16 processors, but still maintainefficient execution on 2 or 4 processors, which would necessitatemanually re-implementing the parallelization. One prior art approachthat attempts to address this issue is the use of a case structure withrespective cases specified for each parallelization case, e.g., 2, 4,16, and so on. However, this approach is also error prone, difficult towrite/maintain, and results in program code that is not aestheticallypleasing. Note that FIG. 6B illustrates the concept of parallelization,but that some embodiments of the automatic parallelization techniquesdisclosed herein may not display the generated parallel loops, i.e., thegenerated second data flow program portions. In other words, theimplementation of the parallel “sub-loops” may be transparent to users.

Various embodiments of methods for automatically parallelizing iterativedata flow program structures, e.g., FOR loops, are described below.Generally, the user may specify which loops should become parallelloops. Then, for each of these loops, an analysis pass may be made tosee if there are any parallelism-breaking dependences. If the analysisdetermines that each iteration of the loop is actually independent ofthe other iterations, a transform, e.g., an index set splittingtransform, may be performed to split the loop's iteration space, i.e.,to parallelize it, so that the iterations will run in parallel. This candramatically improve performance on multi-processor (e.g., multi-core)systems if the amount of computation per iteration outweighs themulti-threading/parallelization overhead.

FIG. 7—Flowchart of a Method for Modifying a Data Flow Program forConcurrent Execution

FIG. 7 is a flowchart of a method for modifying a data flow program forconcurrent execution, according to one embodiment. The method shown inFIG. 7 may be used in conjunction with any of the computer systems ordevices shown in the above figures, among other devices. In variousembodiments, some of the method elements shown may be performedconcurrently, in a different order than shown, or may be omitted.Additional method elements may also be performed as desired. As shown,this method may operate as follows.

First, in 702, a data flow program may be stored, e.g., in a memorymedium, where the data flow program has a first data flow programportion, and where the first data flow program portion is iterative. Inother words, the first data flow program portion comprises an iterativeprocessing structure or code that specifies or implements iterativeexecution of data flow program code. For example, in one embodiment, thefirst graphical data flow program portion may be or include a loopgraphical program structure. Note that in various embodiments, the dataflow program may be a text-based data flow program, or may be agraphical data flow program.

For example, in one embodiment, the data flow program is a graphicaldata flow program that may be displayed on a display device, e.g., acomputer monitor of a computer system, and that includes a plurality ofinterconnected nodes that visually indicate functionality of thegraphical data flow program. The graphical data flow program thus has afirst graphical data flow program portion, where the first graphicaldata flow program portion is iterative. For example, the first graphicaldata flow program portion may be or include a loop graphical programstructure.

In graphical data flow program embodiments, the first graphical dataflow program portion, e.g., the graphical program loop structurepreferably includes an interior, and is configured to iterativelyexecute graphical program code comprised in the interior. In someembodiments, the first graphical data flow program portion, e.g., thegraphical program loop structure, may be a graphical program node, e.g.,a graphical loop node. For example, the node may include an icon with aloop border that encloses the interior (and any graphical program codecontained therein). The loop border, which may be referred to simply asthe “loop”, along with its contained code, may be referred to as thebody of the loop node or structure. In preferred embodiments, the firstgraphical data flow program portion may be or include a FOR loop, andthe node may be a FOR loop node, although other types of paralleliterative processing nodes are also contemplated. For example, in caseswhere the loop is a “while loop”, but where the total number ofiterations to be performed may be determined prior to runtime, the whileloop may be automatically converted to a FOR loop node, according toembodiments described herein.

Moreover, in some embodiments, the FOR loop may be a parallel FOR loop,which denotes a FOR loop that is either marked for (attempted) automaticparallelization, or in some embodiments, that has already beenparallelized. Similarly, the graphical FOR loop may be or include aparallel graphical FOR loop, e.g., a parallel graphical program loopstructure. In some embodiments, a parallel FOR loop may includeadditional elements, structures, or configuration/interfacefunctionality, e.g., border nodes, as described below.

For example, in some embodiments, the graphical data flow program mayinclude a graphical indicator that specifies to a compiler that thecompiler is to attempt to automatically generate data flow program codethat parallelizes a specified portion of the graphical data flow programfor concurrent execution, e.g., the first portion of the graphical dataflow program. In some embodiments, the graphical indicator may be usedby the developer to specify such parallelization. Further detailsregarding embodiments of the graphical indicator are presented below.

Note, however, that the structures, elements, indicators, or nodesdescribed herein may be referred to by any names desired, so long as thefunctionality described herein according to various embodiments isimplemented.

The graphical data flow program may be created on the computer system 82(or on a different computer system). The graphical program may becreated or assembled by the user arranging on a display a plurality ofnodes or icons and then interconnecting the nodes to create thegraphical program. In response to the user assembling the graphicalprogram, data structures may be created and stored which represent thegraphical program. The nodes may be interconnected in a data flowformat, and may comprise a block diagram and may also include a userinterface portion or front panel portion. Where the graphical programincludes a user interface portion, the user may optionally assemble theuser interface on the display. As one example, the user may use theLabVIEW graphical programming development environment to create thegraphical program.

In an alternate graphical embodiment, the graphical program may becreated in 702 by the user creating or specifying a prototype, followedby automatic or programmatic creation of the graphical program from theprototype. This functionality is described in U.S. patent applicationSer. No. 09/587,682 titled “System and Method for AutomaticallyGenerating a Graphical Program to Perform an Image ProcessingAlgorithm”, which is hereby incorporated by reference in its entirety asthough fully and completely set forth herein. The graphical program maybe created in other manners, either by the user or programmatically, asdesired. The graphical program may implement a measurement function thatis desired to be performed by the instrument. More generally, in variousembodiments, the graphical program may be configured to perform one ormore of: an industrial automation function, a process control function,or a test and measurement function, among others. Various examples ofgraphical data flow programs according to embodiments of the presentinvention are provided below in the Further Embodiments section.

The data flow program may be deployable to a target execution platformwith concurrent processing capabilities. For example, the targetexecution platform may include one or more of: one or more multi-coreprocessors, one or more hardware multi-threaded processors, one or moremulti-processor computers, or two or more networked computers.

In 704, the data flow program may automatically be analyzed. As notedabove, it is important that there be no dependences between iterations,i.e., that the iterations may be performed independently of one another.Thus, in some embodiments, automatically analyzing the data flow programmay include automatically performing dependence analysis of the firstdata flow program portion. Dependence analysis refers to analysis ofdependences (or dependencies) between program elements, includingdependences between iterations of iterative program code.

In one embodiment, dependence analysis and reduction operation analysisof the data flow program may be automatically performed, e.g., viasoftware executing on the computer system, i.e., programmatically.Reduction operation analysis refers to analysis regarding operationsthat collect and combine or merge results from separate processes, e.g.,concurrent processes, program portions, etc., to generate reduced ormerged results, and may include dependence analysis regarding thereduction operations. However, it should be noted that reductionoperation analysis may involve more than just data/order dependenceanalysis. It may also require interpreting operations performed byparticular program elements, e.g., data flow nodes, to determine if theyare reduction operations, and to infer or otherwise determine theappropriate initialization values for particular reduction operations.

Performing dependence analysis and reduction operation analysis of thedata flow program may include determining that the first data flowprogram portion cannot be parallelized as specified, and indicating oneor more errors preventing parallelization or one or more warningsregarding parallelization. In one embodiment, indicating the one or moreerrors may include indicating data flow program code that caused thedetermined errors or warnings. For example, the data flow program codethat caused the errors or warnings may be indicated by providinglocation or address information specifying the offending code, or theoffending data flow program code may itself be displayed, among otherindication means.

In some embodiments, user input selecting at least one error of the oneor more errors or at least one warning of the one or more warnings maybe received, and the data flow program code may be indicated inresponse, i.e., in response to the user input selecting at least oneerror of the one or more errors or at least one warning of the one ormore warnings. In other words, the user may select an error or warning,e.g., with a pointing device such as a mouse, and the corresponding dataflow program code (that caused the error or warning) may be indicated,e.g., displayed.

Example errors may include, but are not limited to, errors indicatingconditions regarding: breaking a loop condition, use of shift registers(e.g., except for simple reduction operations and non-overlapping arrayaccesses), array accesses to the same element on different iterations,where at least one access is a write, event structures, and/or controlsor indicators, among others. Exemplary warnings may include, but are notlimited to, warnings indicating conditions regarding: non-reentrantand/or non-functional subVIs (subroutines or subprograms), property orinvoke nodes, primitive nodes with side effects (e.g., not“functional”), e.g., notifiers, queues, FIFO, timing, file I/O, DAQ,TCP/UDP, etc., among others.

Note that some of these conditions may be qualified. For example, intypical looping structures, shift registers (specified memory) may beused to communicate information from one iteration to another, e.g.,between successive iterations, such as a running sum, etc., and thus theuse of shift registers typically precludes parallelization of theiterations. However, in some cases the shift registers may be usedsafely, e.g., access (reads/writes) to the shift register may bepossible without disturbing the parallelization of the iterations. Forexample, in some embodiments, parallelism may be permitted in thepresence of safe (disjoint) read/writes on an array in a shift register.In one embodiment, analysis, e.g., an Omega test, described below, mayallow parallelization in the presence of safe (disjoint) reads/writes onan array whether in a shift register or tunneled in otherwise.

Additionally, in some embodiments, user input modifying the data flowprogram code may be received in response to the one or more errorspreventing parallelization or one or more warnings regardingparallelization. Said another way, in response to the error(s) orwarning(s), the user may modify the data flow program, e.g., theoffending data flow program code that caused the error or warning,although it should be noted that in some cases, the user may,additionally, or instead, modify some other portion of the data flowprogram to resolve the error or warning.

Moreover, further dependence analysis and reduction operation analysisof the data flow program may be performed after such modifying. In otherwords, once the data flow program has been modified, the modified dataflow program may be analyzed again. In some embodiments, anymodification of the data flow program may cause or invoke furtherdependence analysis and reduction operation analysis, because themodifications may or may not have resolved the errors or warnings, ormay have introduced new conditions that might generate further errors orwarnings.

Thus, more generally, the dependence analysis and reduction operationanalysis of the data flow program may be performed in an iterativemanner, where each time the program is modified, the analyses may beperformed.

Such dependence analysis and reduction operation analysis may bedirected to any of various aspects of the data flow program, e.g., thefirst data flow program portion. For example, in one embodiment, theanalyses may include automatically determining any side effects of thedata flow program included in the first data flow program portion,where, side effects refer to (usually untended) consequences of programcode execution not explicitly generated or intended as a program result.Thus, it may be the case that the explicit results are correct orreliable, but there may be side effects that may render theimplementation invalid or undesirable. Alternatively, the side effectsmay simply be something the user should be aware of, and may or may notbe acceptable.

As another example, the analyses may include detection ofcross-iteration dependences that would prevent parallelization, i.e.,dependences between iterations of the first data flow program portion.For example, it may be the case that each iteration (except the first)depends upon the results of the previous iteration, and so none of theiterations can be performed concurrently.

As a further example, performing dependence analysis of the data flowprogram may include recognizing an early termination condition thatprevents parallelization. For example, it may be the case that theexecution of certain iterations depends on whether the terminationcondition in a previous iteration was met, causing a dependence betweeniterations.

In yet another embodiment, performing dependence analysis of the dataflow program may include determining any conflicting array accessesacross iterations of the first data flow program portion. For example,determining conflicting array accesses across iterations of the firstdata flow program portion may include determining an integer linearprogramming problem (ILP) that corresponds to each pair of arrayaccesses in the first data flow program portion, then determiningwhether there is a feasible solution to each ILP, where if there is nofeasible solution to any of the ILPs, then there are no conflictingarray accesses across iterations of the first data flow program portion.

In one embodiment, the data flow program may include one or more arrayaccess operations, and determining conflicting array accesses acrossiterations of the first data flow program portion may include analyzingeach array access operation. More specifically, for each array accessoperation, a source set of operations may be determined, comprising theset of operations that define some or all input values for the arrayaccess operation. A destination set of operations may also be determinedfor the array access operation, comprising the set of operations thatuse some or all output values of the array access operation.Automatically performing dependence analysis and reduction operationanalysis of the data flow program may include analyzing each of the oneor more array access operations, including the source set of operationsand the destination set of operations for each array access operation.

More specifically, in one embodiment, determining any conflicting arrayaccesses across iterations of the first data flow program portion mayinclude: for each array access operation, determining a list of one ormore read expressions representing a set of array elements from whichthe array access operation may read, and determining a list of one ormore write expressions representing a set of array elements to which thearray access operation may write. Performing dependence analysis andreduction operation analysis of the graphical data flow program may theninclude analyzing each of the one or more array access operations,including the one or more read expressions and the one or more writeexpressions for each array access operation.

Similarly, in embodiments where the data flow program is a graphicaldata flow program, such array access operations may be implemented andperformed via array nodes. In other words, the graphical data flowprogram may include one or more array nodes configured to perform arrayaccess operations. In these embodiments, determining any conflictingarray accesses across iterations of the first graphical data flowprogram portion may include: for each array node, determining a sourceset of nodes, comprising the set of nodes that define some or all inputvalues for the array node, and determining a destination set of nodes,comprising the set of nodes that use some or all output values of thearray node. Performing dependence analysis and reduction operationanalysis of the graphical data flow program may then include analyzingeach of the one or more array nodes, including the source set of nodesand the destination set of nodes for each array node.

More specifically, determining any conflicting array accesses acrossiterations of the first graphical data flow program portion may include:for each array node, determining a list of one or more read expressionsrepresenting a set of array elements from which the array node may read,and determining a list of one or more write expressions representing aset of array elements to which the array node may write. As above,performing dependence analysis and reduction operation analysis of thegraphical data flow program may include analyzing each of the one ormore array nodes, including the one or more read expressions and the oneor more write expressions for each array node.

It should be noted that a single array write operation may conflict withitself across different iterations of a loop, and so in some cases, theabove analysis may be directed to, or may detect, a single array accessoperation.

In 706, program code implementing a plurality of second data flowprogram portions may be generated, e.g., automatically generated, basedon the first data flow program portion, where each of the second dataflow program portions is configured to execute a respective one or moreiterations. In one embodiment, the program code implementing a pluralityof second data flow program portions may be generated based on the firstdata flow program portion and the analysis (or analyses) describedabove. Note that as used herein, “automatic” means that the action isperformed by software, i.e., programmatically, and thus does not requiredirect user involvement, although the action may (or may not) be invokedor configured by the user.

In one embodiment, each of the second data flow program portions is amodified version of the first data flow program portion. Thus, in someembodiments where the data flow program is a graphical data flowprogram, each of the second data flow program portions may be a modifiedversion the first graphical data flow program portion. However, itshould be noted that in some embodiments, these modified versions of thefirst graphical data flow program portion may not be displayed.

In graphical data flow embodiments where the graphical data flow programincludes a graphical indicator specifying that parallelization is to beattempted, the automatic generation of program code implementing theplurality of second data flow program portions may be performed based onthe graphical indicator. Further details of the graphical indicator andits functionality according to various embodiments are provided below.

The plurality of second data flow program portions may be configured toexecute at least a portion of iterations concurrently during executionof the data flow program. Moreover, execution of the plurality of seconddata flow program portions may be functionally equivalent to sequentialexecution of the iterations of the first (possibly graphical) data flowprogram portion. In other words, the cumulative results of executing theplurality of second data flow program portions may be the same asresults that would have been produced by sequential iterative executionof the first data flow portion. Note that as used herein, “concurrently”means that at least a portion of the concurrent processes overlap intime, i.e., at least one of the instances must execute at least oneiteration while another instance executes another iteration.

The method may further include executing the data flow program,including each of the second data flow program portions executing therespective one or more iterations, where the plurality of second dataflow program portions collectively execute all iterations specified forthe first data flow program portion.

Note that the program code implementing the plurality of second dataflow program portions may be automatically generated in response tothere being no detected conditions preventing parallelization of thefirst data flow program portion. In other words, the program code may beautomatically generated contingent upon the parallelization beingfeasible, i.e., reliably implementable. The absence of such conditions(preventing parallelization) may be determined via analysis of the dataflow program, as described in more detail below.

Further Embodiments

Below are provided further details regarding embodiments of the methoddescribed above with reference to FIG. 7. It should be noted that thevarious embodiments described below are meant to be exemplary, and arenot intended to limit the elements described to any particular features,functions, or appearances.

Received Information

In some embodiments, information may be provided or received that mayaid in the analyses and/or code generation described above. For example,in one embodiment, information specifying parallelism for the data flowprogram may be received, where the program code implementing a pluralityof second data flow program portions is automatically generated based onthe first data flow program portion and the received information. Forexample, the information specifying parallelism for the data flowprogram may specify one or more of: data flow program portions toparallelize, number of second data flow program portions to generate, oran iteration scheduling strategy specifying how the index blocks ofiterations are to be distributed among the plurality of second data flowprogram portions.

Note that the scheduling strategy may affect how the code is generated,and how the parallelism is implemented. For example, in one embodiment,the iteration scheduling strategy may be specified as a static schedule,where each second data flow program portion is statically assigned arespective one or more index blocks of the iterations. Examples ofstatic scheduling include blocked and blocked cyclic scheduling. Inblocked scheduling, each second data flow program portion, which may bereferred to herein as a “worker” for brevity, is allocated one block (of0+ iterations), such that for P workers, there are P blocks scheduled,e.g., evenly divided, to cover all of the iterations. In blocked-cyclicscheduling, the iteration block size is specified, then the blocks aredistributed in round-robin fashion (statically scheduled atcompile-time) to each of the workers. Thus, for N iterations, P workers,and a block size of C, there may be N/C blocks distributed among the Pworkers (as allowed by the values of N, C, and P), and each worker willbe allocated N/(P*C) blocks (rounded up or down), or, N/P iterations onaverage.

As indicated above, in another embodiment, the iteration schedulingstrategy may be specified as a dynamic schedule, where each second dataflow program portion is dynamically assigned a respective one or moreindex blocks of the iterations during runtime in an opportunisticmanner. Further details of static and dynamic scheduling are providedbelow

Thus, in some embodiments, the number of second data flow programportions to generate may be determined dynamically at runtime, and somay not need to be specified by this information. However, in oneembodiment, such information (specifying the number of second data flowprogram portions to generate) may be used to set a maximum parallelismlimit for the dynamic allocations, i.e., may specify an upper bound forthe number of second data flow program portions to generate.

In one embodiment, user input specifying one or more constraints on themulti-processing functionality may be received, and the iterationscheduling strategy may be executed subject to the user specified one ormore constraints. For example, the user may constrain the number ofsecond data flow program portions to generate, as mentioned above. As aslightly more sophisticated example, the user may specify that thenumber of second data flow program portions to generate should be theminimum of a statically specified number and a dynamically determinednumber. Further examples of such user-specified constraints includespecifying a fixed or minimum blocksize for [C], e.g., fixed for astatic schedule or fixed-size dynamic schedule, and minimum for thedynamic decreasing schedule (e.g., down to a minimum C).

In some embodiments, information specifying multi-processingfunctionality of an execution platform for the graphical data flowprogram may be received, where the program code implementing a pluralityof second data flow program portions distributes iterations among thesecond data flow program portions based on inputs to the first graphicaldata flow program portion and the received information. Examples ofinputs (used to distribute iterations) include input to [N] and incomingarray data, which may help determine the number of actual iterations toexecute.

Exemplary items that may be specified by the information specifyingmulti-processing functionality of the execution platform include one ormore of: number of processing cores of the execution platform (or moregenerally, number of processing elements), number of hardware executionthreads per processing core, a number of second data flow programportions to use at run-time, or a minimum index block size for iterationscheduling, among others. More generally, the information may specifyany attribute germane to the multi-processing functionality of theexecution platform, as desired. In some embodiments, the method mayinclude querying the execution platform, and receiving the informationspecifying multi-processing functionality of the execution platform fromthe execution platform in response to the query. Additionally, orinstead, the query may be made to a database of such information.

The information may then be used to allocate iteration index blocksamong the second data flow program portions. For example, the number oflogical processors available for executing iterations concurrently maybe determined by multiplying the number of processing cores of theexecution platform times the number of hardware execution threads perprocessing core. Note that in some embodiments, some of these items willnot typically be specified together. For example, the receivedinformation may not specify both the number of processing cores and thenumber of execution threads, since the number of processing elements maydetermine the number of threads, and the user can specify T blocks ofiterations (where T is an integer), e.g. splitting an array into Tchunks or blocks, and one or more processing structures, e.g., threads,may be assigned to each processing element, which will consume the Tblocks as determined by the schedule.

In one embodiment, the user may explicitly provide as input, e.g., “wirein”, a positive (non-zero) integer specifying the execution threadcount, i.e., the number of execution threads, although other means ofspecifying this number are also contemplated, as will be discussedbelow. For example, the user may wish to assign half the availableprocessing elements to each of two parallel loops in the graphicalprogram, and so may specify this explicitly via an input wire to theloop node. While in some embodiments, the number of threads may be equalto the number of processing elements, e.g., by default, in otherembodiments, this may not be the case, although the number of threadsallowed may have a specified maximum, e.g., equal to the number ofprocessing elements, or some multiple of this value, e.g., 4×the numberof processing elements, etc., as desired.

It should be noted that the term “thread” is used herein in its genericsense, and is intended to refer to any of various execution mechanismswhereby operations or tasks maybe performed or executed in parallel,i.e. concurrently in a controlled fashion. As used herein, a “block”refers to a contiguous set of iterations of a loop that may be allocatedto a processor for execution. Similarly, the term “array block” may beused to refer to a corresponding array subset, e.g., a contiguous subsetof a data structure used to store data for and/or of these iterations.Note that, as indicated above, in various embodiments, the targetexecution platform may be or include one or more of: one or moremulti-core processors, one or more multi-processor computers, or two ormore networked computers. In other words, the target platform maybe anykind of computing system that includes multiple processing elements, bethey processing cores, processors, or processing devices.

The allocation portion of the iterations, which may be referred to asblock size, i.e., how many contiguous iterations to dole out at a time,may be explicitly specified by the user. Thus, for example, for 4threads operating on an array of 100 floats, the user could specify thateach thread take on blocks of 8 elements at a time (e.g., perhaps basedon the size of a cache line, thereby yielding better cache locality),instead of, say, a default of 25 elements/iterations per thread.Alternatively, the elements/iterations could be blocked so that the datafor each block fits inside a single processing element's cache. In someembodiments, the block size may be a minimum block size or alignmentparameter, such that the distributed blocks are actually a multiple ofthe (minimum) block size. This may accommodate alignment concernswithout naively using unnecessarily small blocks and thus creatingexcessive overhead.

As indicated above, there are various ways in which the informationdescribed above may be received. For example, in one embodiment, userinput specifying the multi-processing functionality may be received,e.g., via a graphical user interface (GUI) of the program developmentenvironment, where, for example, the user may provide the input to adialog box or wizard, or by wiring inputs to the node, among other inputtechniques. Alternatively, or in addition, in one embodiment, receivinginformation specifying multi-processing functionality of a targetexecution platform may include querying the execution target platform(or some other resource, e.g., a database of execution platforminformation), and receiving the information specifying multi-processingfunctionality of the target execution platform from the execution targetplatform in response to the querying. As another example, the method mayinvolve simply retrieving default information specifyingmulti-processing functionality of a target execution platform for thegraphical program, where, for example, a user or subsequent process maymodify or override this information.

FIGS. 8A-8B—Border Nodes

In some embodiments, border nodes may be implemented for specifyingand/or denoting parallelization attributes or parameters of FOR loops,where the term “border node” refers to the placement of the node (orterminal) on the border of a graphical FOR loop. However, it should benoted that the functionality of any of the graphical elements disclosedherein may be implemented in other forms, e.g., a textual programelements.

FIG. 8A illustrates an exemplary FOR loop that includes a border node802 whereby parallelization may be specified for the FOR loop. In theembodiment shown, the border node 802, denoted “P” in the figure, issituated on the upper left edge of the FOR loop just under the loopcounter N, and includes an outer terminal to which the user canexplicitly wire a positive (nonzero) integer to specify the number ofworkers (second data flow program portions) to implement for concurrentexecution of loop iterations. For example, the user may need to allocatehalf of available processing elements (e.g., processors) among twoparallel FOR loops. As may be seen, in this case, the value wired to theouter terminal is 8. This parameter may be useful for scalabilitytesting.

The border node may also include a static upper bound parameter viawhich the user may specify an upper bound on the number of workers to beimplemented, e.g., at compile time. In one embodiment, the user mayspecify the upper bound at compile-time on a per-loop basis through aconfiguration dialog box, e.g., via a Number of Generated Parallel LoopInstances in the For Loop Iteration Parallelism Configuration Dialog,possibly with a global default value (e.g., 4 or 8) set by an INI(initialization) token. To prevent excessive compilation time, the valueof this upper bound may itself have an upper bound, e.g., 128.

The border node may also include an inner terminal whereby the actualworker count may be denoted or specified. For example, this value may beset to the minimum of the dynamic user-specified value (if wired) andthe static upper bound, and may be rounded up to 1 if the user specifiesa value less than 1.

Thus, for example, consider a scenario where the target platform is amachine with 8 cores/processors, and there are two FOR loops, e.g.,parallel FOR loops, on the same diagram, not nested, arranged next toeach other “in parallel”. Each FOR loop may be configured to generate 8loop instances (workers). If [P] is left unwired (e.g., unspecified),the default behavior may be to use the number of processors available atruntime (8) as the value to give [P], and thus 16 worker instances (8from each FOR loop) may be implemented, which will attempt to operateconcurrently. However, since there are only 8 processors available (not16), this arrangement may result in extra thread overhead andsub-optimal performance. A preferred solution for this kind of scenariomay be to utilize a primitive, e.g., a CPU Info primitive, to query thenumber of processors available at runtime (8), then divide that value bythe number of FOR loops on this diagram (2), and wire the result (4) tothe [P] node on each of the FOR loops. Then, even though 8 workerinstances have been generated for each of the FOR loops, only 4 will beused by each, resulting in 8 total worker instances executing inparallel, matching the available parallelism on the machine and yieldingbetter performance than the oversubscribed (8+8) version.

In one embodiment, a [C] border node, which may also be referred to as a[C] terminal, may be used with or on the FOR loop, e.g., under the [P]border node (or terminal). Note that some border nodes may includemultiple terminals, e.g., an external terminal for wiring elements,e.g., values, from outside the FOR loop, and an internal terminal forwiring a value to or from an element inside the FOR loop.

More generally, a border node is a node that lives on a structure (e.g.,a FOR loop) between its inner diagram(s) and the structure's parentdiagram outside, and may have input and output terminals. For example,the [N] border node specifies the number of iterations to be performedby the structure. The [P] border node has one input terminal coming fromthe loop's parent diagram, outside of the loop, and one output terminalthat feeds into the loop's inner diagram, and is related toparallelization, as described herein. The [i] border node shown has onlyan output terminal feeding into the loop's inner diagram, and relates tothe loop counter.

For the dynamic fixed blocks schedule, [C] may be used to specify theblock size(s). For the dynamic decreasing blocks schedule, [C] may beused as a minimum block size, e.g., with a value of 1 as a default. Theoutput of [C] may be the actual blocksize of the block containing thecurrent iteration. FIG. 8B illustrates a simplified FOR loop with [P]and [C] (and [N]) border nodes, although this example loop has no innernodes, and may thus not compute any results.

In one exemplary embodiment, there may be three phases regardingmulti-processing information and its use:

Edit-time: If not otherwise specified, the host, i.e.,editing/developing, user's machine may be queried for its number oflogical processors, and this value may be used as the default value forthe number of workers to generate for the initial configuration ofiteration parallelism by the user. Subsequently, the last valuespecified may be used. Note that each first data flow program portion(if there are more than one in the data flow program) may save itspersonal copy of the value specified.

Compile-time: Each first data flow program portion's savednumber-of-workers-to-generate is used to generate that many workers(second data flow program portions) in the executable code for thatfirst data flow program portion.

Run-time: The statically (edit time) specified number of workers arerepresented in the instruction code for the first data flow programportion, and if the user did not encode another value in the program,e.g., by “wiring” a specified value to the first data flow programportion, the execution platform may be queried for its number of logicalprocessors, and the minimum of the static and dynamic values may specifythe number of workers to be used at runtime.

Data Flow Intermediate Representation

In some embodiments, an intermediate representation (DFIR) of the dataflow program may be utilized in the analysis and/or the code generationportions of the method. For example, in one embodiment, the method mayinclude automatically generating a DFIR of the data flow program. Theautomatically performing dependence analysis and reduction operationanalysis of the data flow program may include automatically analyzingthe data flow intermediate representation of the data flow program.Similarly, automatically generating program code implementing theplurality of second data flow program portions may include generatingexecutable code based on the data flow intermediate representation. Inother words, rather than generating the program code implementing thesecond data flow program portions directly, intermediate structures(DFIR structures) may be generated, then the program code may begenerated from these intermediate structures. Thus, in some embodiments,a DFIR (or multiple DFIRs) may be used to perform at least a portion ofthe methods described herein.

Dependence Analysis

As discussed above, a FOR loop cannot be parallelized if it contains anyside effects or cross-iteration dependences, and so a dependenceanalysis may be performed on the FOR loops to determine if suchdependences (including side effects) exist. Errors may be generated ifproperly executable code cannot be generated because of a detectedproblem, while warnings may be generated if properly executable code maybe generated but its correctness may not be guaranteed e.g. there may beside effects that are out of order, i.e., that do not preserve thetransparency of the parallelization. In preferred embodiments, thedependence analysis occurs at edit-time/type propagation, so the usercan receive immediate feedback. In various embodiments, the analysis maybe performed by the development environment, or by a separate tool,described in more detail below.

The analysis techniques that may be used to determine whether or notparallelism of a FOR loop is possible are numerous and varied, any ofwhich may be used as desired. In some embodiments, the dependenceanalysis may include determining any conflicting array accesses acrossiterations of the graphical program code comprised in the interior,where if there are conflicting array accesses across iterations of thegraphical program code comprised in the interior, the iterations of thegraphical program code are not parallelizable.

FIG. 9 illustrates an exemplary graphical program for matrixmultiplication that includes three nested FOR loops. As shown, matricesA, B and C are pre-allocated outside of the loop by respective graphicalprogram nodes labeled accordingly (in boxed text), and passed into thecomputation loops by tunnels and shift registers. Note that thisimplementation utilizes shift registers; more specifically, an inplacealgorithm inplaces the shift registers across the loops. There are noextra memory copies of the array inside the triple-nested loops, butbecause of the usage of shift registers, initial analysis may suggestthat the loops are therefore non-parallelizable. However, from basicknowledge of linear algebra, it is clear that all three loops can beparallelized. Note, however, that while any of the three loops can beparallelized, the outermost loop may be preferred because it providesthe highest-granularity for the parallelism. For example, parallel innerloops would have to synchronize at the end of each of their outer loop'siterations, which may leading to less scalable parallelism. Thefollowing describes details of an analysis technique that can properlydetermine the parallelizability of such FOR loops and others.

Embodiments of the data flow and array disambiguation analysis describedherein may enable automatic discovery of parallelizable loops, and insome embodiments, parallelization of them, thereby freeing developersfrom the tedious and error prone process of manual analysis and/orparallelization. The developers can focus their efforts on algorithmdevelopment in sequential order, then the analysis and transformationtools described herein can take over the sequential code andautomatically detect the parallelizable loops and parallelize them. Notethat these tools may facilitate automatic parallelization of legacycodebases.

As discussed above, a core idea of the analysis is to determine whetherthere exist any conflicting accesses of the array elements across theloop iterations. If there are conflicting array accesses, the loop doesnot allow parallelism. Otherwise, the loop may or may not allowparallelism, depending on other attributes of the program.

Two simple yet illustrative diagrams are shown in FIG. 10 and FIG. 11.FIG. 10 shows an example of a parallelizable loop. For every iterationin the loop (FIG. 10), the array index node reads the (2*i+1)^(th)element and the array replace element node writes to the (2*i)^(th)element. The problem of deciding whether there are any conflicting arrayaccesses may be approached as a problem of determining whether there isa feasible solution to an Integer Linear Programming Problem (ILP), asdiscussed briefly above.

For example, for the loop in FIG. 10, the underlying ILP problem is:

1+2*x2=2*x1, subject to the following constraints:

0<=x1

0<=x2

x2!=x1

Straightforward analysis indicates that there is no feasible solution tothis ILP. Therefore, the loop may be parallelizable, depending on otherfactors.

FIG. 11 shows an example of a non-parallelizable loop. For everyiteration in the loop, the array index node reads the (2*i+1)^(th)element and the array replace element node writes to the (3*i)^(th)element. The underlying ILP for this loop is:

3*x2=1+2*x1, subject to the following constraints:

0<=x1

0<=x2

x1!=x2

This problem is feasibly solvable. For example, (x2=3, x1=4) is asolution, indicating that the result produced at the 3rd iteration isused at the 4th iteration. Therefore, this loop is not parallelizable.

From the above examples, it can be seen that the essential approachunderlying the array disambiguation analysis is to test whether there isa feasible solution to an ILP. Any of various algorithms for solvingsuch underlying ILPs may be used as desired. In one embodiment, WilliamPugh's Omega test algorithm (using branching-bounding approaches) may beused to solve the underlying ILP. The details of one embodiment of thisalgorithm follow:

Pugh's Omega Test

(1) Choose a variable in ILP to eliminate. The algorithm uses theFourier-Motzkin variable elimination method, although other methods maybe used as desired. The idea is to apply substitution and simplificationon the original ILP so that the range of linear coefficients in the newILP is decreased compared to the original (or previous) ILP. An exampleof this variable elimination is shown in Table 1 below. In step 1,variable x is substituted away. Note that the maximum absolute value ofthe coefficient in the original ILP is 31 and the maximum absolute valueof the coefficient in the new ILP is decreased to 24.

(2) Eliminate the variable and calculate the real and dark shadows ofthe set of constraints along that dimension. A real shadow is therelaxed region that covers the true solution region. A dark shadow is aconstrained region that lies within the true solution region.

(3) If the real and dark shadows are the same, there is a feasiblesolution for the original problem if and only if there is an integersolution to the problem in the shadow.

(4) Otherwise:

-   -   (a) If there are no integer solutions in the real shadow, there        is no solution to the original problem.    -   (b) If there are integer solutions in the dark shadow, there is        a solution to the original problem.    -   (c) Otherwise, it is known that if there exists an integer        solution, it must be closely nested in the upper bound and lower        bound of the eliminated variable. Therefore, the original        problem may be replaced with a set of sub-problems, and the        sub-problems may be tested. The sub-problems may enumerate every        possible value between the dark shadow and real shadow. There is        no feasible solution if and only if there is no solution to any        problems in the set. In other words, in (c), the original        problem may be transformed into a set of new problems. This is        the most computationally expensive case, which may result in an        exponential number of problems to solve. However, this rarely        happens in real applications. Essentially, the inequality        constraint is replaced by equality constraints that enumerate        every possible value that lies in between the dark and real        shadows. For example, consider a case where the real shadow of a        2D constraint is 3x+2y<=3 and the dark shadow of the 2D        constraint is 3x+2y<=5. Then, three new problems may be created        with equality constraints {3x+2y=3, 3x+2y=4, 3x+2y=5},        respectively. These new constraints are illustrated as 3 lines        in FIG. 12. A high level intuitive description of the algorithm        is as follows: If a solution can't be found in the real shadow        (relaxed problem), there is no solution. If a solution is found        in the dark shadow (constrained problem), there is a solution.        When a solution is found in the real shadow but not in the dark        shadow, determination of whether there is a solution or not        requires further tests. In such case, the problem may be broken        down into a set of sub-problems and the sub-problems checked. In        the graph of FIG. 12, the sub-problems are the lines to check,        i.e., checks are made as to whether there are solutions on those        3 lines.

TABLE 1 Omega Test Example Substitution Problem Original problem 7x +1y + 31z = 17 3x + 5y + 14z = 7 1 <= x <= 40 −50 <= y <= 50 X = −8a − 4y− z − 1 −7a − 2y + 3z = 3 −24a − 7y + 11z = 10 1 <= −8a − 4y − z − 1 <=40 −50 <= y <= 50 Y = a + 3b −3a − 2b + z = 1 −31a − 21b + 11z = 10 1 <=−1 − 12a − 12b − z <= 40 −50 <= a + 3b <= 50 Z = 3a + 2b + 1 2a + b = −11 <= −2 − 15a − 14b <= 40 −50 <= a + 3b <= 50 b = −2a − 1 1 <= 12 + 13a<= 40 −50 <= −3 − 5a <= 50 Final result 0 <= a <= 2 (feasible)Exemplary Implementation:

As indicated above, in some embodiments, the array analysis may beimplemented in a DFIR of the data flow program. For example, theanalysis may be performed just after the data flow program, e.g., thegraphical data flow program, is lowered or transformed into a DFIRgraph. The result of the analysis may then be available for subsequentcompilation, transformation, and optimization, e.g., looptransformations, inplace algorithm, etc. The analysis may also be usedas a feedback tool to the end user. In one embodiment, the detectedparallelizable loops may be displayed graphically to the user. Fornon-parallelizable loops, visualization of the analysis result mayinclude showing the programmer the exact conflict array accesses thatdisallow the parallelization. With this information, the user may beable to restructure those non-parallel loops and make them parallel. Insome embodiments, this analysis may be provided or implemented in aprogram analysis tool or toolkit to provide an analysis tool forparallel loop detection.

In one embodiment, the array analysis process or tool may be implementedby or include the following components or modules, where the parallelloop detection component may be the main application module that usesthe other components. Note, however, that the particular organization ofthe functionality (and possibly portions of the functionality itself) ismeant to be exemplary only, and that any other arrangements orarchitectures may be used as desired.

(1) Loop annotation: This component annotates some basic loopinformation for linear expression system and parallel loop detection,e.g., the ID of the loop, the set of induction variables in the loop,the nesting level of the loop, and the range of the induction variables,among others. It should be noted that the annotations described hereinmay be included in the programs themselves, in DFIRs of the programs, orin separate data structures, e.g., distinct from the programs or DFIRS,as desired. Moreover, in some embodiments, while each of these items ofinformation may be required to perform the analysis, some or all of thisinformation may be “built-in” to the programs or intermediaterepresentations thereof, and so may not necessarily have to be computedor annotated.

(2) Expression formation/propagation: This component constructs andpropagates the linear expression in the DFIR graph. For example, thelinear expression may be represented as a std::map, which may containthe variable ID and its coefficient pair.

(3) Data flow algorithm for source/destination array set: This componentpropagates the array data flow information in DFIR. For each array node,it may annotate the “source” set and the “destination” set. The “source”set is the set of nodes which define some or all the values for thecurrent node. The “destination” set is the set of nodes which use someor all the values produced by the current node. The source anddestination sets plus the array access expression constructed bycomponent 2 may be used together for the detection of array accessconflicts in the parallel loop detection module.

(4) Omega test: This module solves the ILP, using the Omega testalgorithm described above to decide whether there is a feasible solutionto the ILP or not. As noted above, other embodiments may use otheralgorithms to perform this test, as desired.

(5) Parallel loop detection: This is the main application module forparallel loop detection, and may analyze each loop in the diagramindividually. More specifically, it may collect all the array accesseswithin the loop, build up the ILP problems for every possible pairs ofarray accesses, and run the Omega test to determine whether there is anyarray accesses conflict. If no conflict array accesses are detected, theloop may be safe to parallelize; otherwise the loop isnon-parallelizable.

It may be instructive to describe a walk-through of the algorithm asapplied to a graphical data flow program, e.g., an example LabVIEWdiagram. Consider an LU matrix decomposition as the example. As is wellknown, LU decomposition is used in numerical analysis to solve systemsof linear equations or calculate a determinant. More specifically, LUdecomposition computes: A=LU, where L and U are the lower triangular andupper triangular matrices, respectively.

FIG. 13A illustrates an exemplary diagram to compute the L matrix, andshows the annotation array access expressions in the loop. In thisembodiment, L is stored to the lower triangular of A (L\A) and themultipliers computed for the row subtraction are stored in the uppertriangular of A (A\M). The decomposition algorithm starts from theupper-left of the matrix and walks towards the bottom-right of thematrix. FIGS. 13A-13D illustrate steps of one embodiment of arrayanalysis performed on the diagram of FIG. 13A, i.e., the work flow ofarray analysis on the LU decomposition diagram of FIG. 13A. FIGS.13B-13D show the example ILP and the analysis applied to the 3 nestedloops individually. The dashes boxes in each figure show the arrayread/write access expressions from which the ILP is constructed. ExampleILPs constructed for one pair of array accesses for each diagram aredescribed with each figure.

FIG. 13B illustrates application of the Omega test and parallel loopdetection for the outermost loop. The example ILP for FIG. 13B is:

<I₁″+I₂″+1, I₁″+I₃″+1>==<I₁′, I₁′>?

Subject to the constraints:

0<=I₁″<N; 0<=I₁′<N;

0<=I₂″<N−I₁″−1; 0<=I₂′<N−I₁′−1;

0<=I₃″<N−I₁″−1; 0<=I₃′<N−I₁′−1;

I₁′!=I₁′.

A feasible solution for this ILP is:

I₁″=I₁′−1;

I₂′=0;

I₃″=0.

Thus, the outer loop has array access conflicts, and cannot beparallelized, as indicated by the label “NONPAR” at the top of the outerloop.

FIG. 13C illustrates application of the Omega test and parallel loopdetection for the middle loop. The example ILP for FIG. 13C is:

<I₁″+I₂″+1, I₁″+I₃″+1>==<I₁′, I₁′>?

Subject to the constraints:

0<=I₁″<N; 0<=I₁′<N;

0<=I₂″<N−I₁″−1; 0<=I₂′<N−I₁′−1;

0<=I₃″<N−I₁″−1; 0<=I₃′<N−I₁′−1;

I₁″=I₁′.

There is no feasible solution for this ILP.

Thus, there are not conflicting array accesses, and so the middle loopmay still be parallelizable, as indicated by the label “PAR” at the topof the middle loop.

FIG. 13D illustrates application of the Omega test and parallel loopdetection for the inner loop. The example ILP for FIG. 13D is:

<I₁″+I₂″+1, I₁″+I₃″+1>==<I₁′, I₁′>?

Subject to the constraints:

0<=I₁″<N; 0<=I₁′<N;

0<=I₂″<N−I₁″−1; 0<=I₂′<N−I₁′−1;

0<=I₃″<N−I₁″−1; 0<=I₃′<N−I₁′−1;

I₁″=I₁′;

I₂″=I₂′.

There is no feasible solution for this ILP.

Thus, there are no conflicting array accesses, and so the inner loop maystill be parallelizable, as indicated by the label “PAR” at the top ofthe inner loop.

Thus, the Omega test gives a yes/no answer regarding the feasibility ofthe ILPs for each loop. Note that the 2 inner loops are (possibly)parallelizable and the outer loop is not parallelizable because theread/write array access conflict.

Scheduling

There are numerous ways in which the scheduling of iteration executionmay be implemented, details of which are now presented.

Static Schedule

As noted above, in various embodiments, the execution schedule may bespecified as a static schedule, where each execution thread isstatically assigned a respective subset of the iterations, or a dynamicschedule, where each execution thread is dynamically assigned respectivesuccessive subsets or blocks of the iterations during runtime in anopportunistic manner.

Note that in the case of a static schedule, which in some embodimentsmay be the default scheduling strategy, each thread may be assignedspecific blocks of elements or iterations to operate on, distributedround-robin to each of the threads. Static scheduling means that eachthread knows exactly which iterations it will execute on startup andthus does not need to coordinate with other threads to operate.

Note that the subset of elements or iterations assigned to a thread mayinclude multiple disjoint subsets, i.e., the elements or iterations ofthe subset may not all be contiguous. For example, a subset may includemultiple blocks, each of which may have contiguous elements/iterations,but which may or may not be contiguous with respect to each other.

Said another way, in a static scheduling strategy, which may be denotedas Static(P,C), the iteration set and input arrays may be split intoblocks of C elements to operate on, with blocks distributed round-robinto each of the P workers. Thus, if the user does not specify c then asimple block distribution may be used; otherwise a block-cyclicdistribution may be used, with blocks of size C.

Note that simple (static) block distribution allocates the iterationsamong P workers by dividing the iterations into P contiguous blocks,which can result in inefficiencies due to the fact that all iterationsmay not perform the same amount of work, and thus require more or lesstime to execute. Thus, partitioning the iterations based on simple blockdistribution may not balance the computational load efficiently amongthe workers. Nor does this strategy allow users to divide the iterationsfor better cache locality. In other words, static scheduling approacheswhere each worker is assigned a fixed-sized block of contiguousiterations from the original FOR loop, and each worker executes the samenumber of iterations, balances the work between iterations when theiterations take the same amount of time to execute and the workers arenot interrupted. However, this static approach does not balance the workwhen the iterations contain variable amounts of work or when theprocessing environment is unpredictable, e.g., this scheduling solutionis not able to adapt if some of the iterations take longer than othersor if some of the workers don't execute as quickly as others.

In contrast, block cyclic distribution splits iterations across workersdynamically, allocating blocks of iterations to each worker at runtime.More specifically, with a block cyclic schedule, which is a staticschedule, the iterations may be divided into blocks or chunks of Citerations, where the user may provide C. The blocks may be distributedamong the workers in a round robin manner. FIG. 14 shows how sixteeniterations may be divided among four processors when C is two, accordingto one embodiment. As may be seen, in this example each worker executestwo blocks of two iterations each. Note that in one embodiment, forblock cyclic distribution, each worker loop may be wrapped in anotherloop that iterates through the blocks for this worker, feeding theblocksize and offset into the inner worker loop.

Thus, in one embodiment, the user may explicitly specify the number ofiterations to dole out at a time. For example, for 4 workers operatingon an array of 100 floating point values, the user may specify that eachworker process blocks of 8 elements at a time (perhaps the size of acache line, thereby yielding better cache locality), instead of thedefault simple block distribution where each of the 4 workers consumesone chunk of 25 elements. Alternatively, the data could be blocked orchunked so that each block fits inside a single processor's cache. Insome embodiments, the blocksize may be a minimum blocksize or alignmentparameter, such that the distributed blocks are actually a multiple ofthe blocksize, allowing consideration of alignment concerns withoutnaively choosing unnecessarily small blocks and creating excessiveoverhead. In one embodiment, the value C may be specified via a bordernode, described below under the section “Border Nodes”.

One variation of a static scheduling strategy is a static (bounded)allocation strategy, in which a fixed number of workers equal to thestatic upper bound K are allocated or implemented, but where theiterations, i.e., the work, may be divided such that only P_actual ofthe workers are utilized, where P_actual is the minimum of P and theupper bound K (discussed above). Note that this approach still suffersfrom a waste of space when K>P and an inability to scale up to more thanK processors. However, for a sufficiently large K, this may affect theparallelism on very few machines.

Another variation of a static scheduling strategy uses a static schedulewith dynamic allocation of iteration blocks. In one embodiment of thisapproach, each worker (second data flow program portion) may becontained in an automatically generated wrapper, e.g., a subVI. Thus,for each worker, a wrapper may be automatically generated that containsa blockable or chunkable version of the original FOR loop. The callingcode can loop through and call this wrapper a specified number of times,e.g., P times, with appropriate inputs for each call. In one embodiment,the wrappers may be reentrant, thus allowing for concurrent invocationand execution. Moreover, each wrapper may use an in-place structure tokeep inputs/outputs in-place to each other. Additionally, input andoutput arrays may be sub-arrays.

Note that the wrapper implementation may suffer from poor performance;however, the code duplication alternative would cause considerable codebloat. Thus, benchmarking may be used to determine which strategy isappropriate for a given application. Further details regarding use ofwrappers for the workers are provided below.

Dynamic Schedule

In contrast to static scheduling, in dynamic scheduling, which may bedenoted by Dynamic(P,C), each thread may be assigned a block of elementsor iterations to operate on, then, whenever a worker needs more work, itis dynamically assigned a next block of elements/iterations. Note thatthis dynamic assignment scheme does not proceed in round-robin order asthe static schedule does. Thus, dynamic scheduling may be implemented tohelp balance the load between workers. With dynamic schedules, theiterations are divided into blocks or chunks, and when a worker finishesits current block, it is assigned another block from the pool. Thisallows workers that finish early to get additional work. For example,with 4 threads, if thread 3 completes its (say) 8-element block beforethread 2, thread 3 may ask the scheduler for the next available blockinstead of simply grabbing a statically pre-designated next block.Dynamic scheduling may thus be particularly beneficial in certain typesof applications.

A simple example of such an application is shown in FIG. 15. As may beseen, a static block schedule would not perform well for the loop shownbelow, since each iteration of the outer loop requires more computationthan the previous iteration, and so the workers that received the lastblocks of iterations would need to perform much more computation thanthe first. The workers with less work would thus sit idle waiting forthe other instances to complete.

Computing the Mandelbrot set is another example of an algorithm wheresome loop iterations take longer than others. FIG. 16 illustratesexemplary output from such an application. The algorithm iterates overpoints in a 2D space to determine whether each point is in the set andcolors the point black if it is in the set. The computation requiresmore steps (iterations) if the point is in the set. Thus, if the points(pixels) of the left side of the space (image) were computed in parallelwith those of the right side, the right half of the image would takelonger to process since more of those points are black.

With a dynamic schedule, the iterations may be assigned to workers whenthey request work. Each loop worker requests a block, computes theiterations, and then requests another block. With this type of schedule,the workers that get more CPU time or blocks with less work execute moreiterations of the original loop.

Three exemplary types of dynamic schedule that may be implementedinclude: Dynamic Fixed Blocks, Dynamic Decreasing Blocks, andUser-Specified Partitioning, among others. The primary differencebetween these strategies is in how the sizes of the blocks aredetermined. The rest of the support code may be identical. Theseexemplary dynamic scheduling strategies are now described.

Dynamic Fixed Blocks

In one embodiment of this form of dynamic scheduling, the iterations maybe divided into constant-sized blocks (with the possible exception ofthe last block, which may contain fewer iterations). The user mayspecify the block size. In some embodiments, the default value may beone (1). In other embodiments, the block size may be computed based onthe data size and cache sizes.

Said another way, in one embodiment, a static number of parallel callsmay be allocated to each reentrant worker wrapper instance. Every blockmay be pushed onto the block queue, and each worker wrapper instance maydequeue a block, execute the FOR loop over the block, and output itsresults (e.g., to another queue), then fetch another block from theinput queue. After the worker wrappers have consumed all blocks and eachhas completed and returned its results, the caller (e.g., program,VI/diagram) may reconstruct the results from the output queue.

In one embodiment, for the dynamic schedule, the FOR loop may beconverted into a scheduler element wrapping multiple calls to the workerwrapper holding the modified (split) original loop body, i.e., thesecond data flow program portion. The scheduler may manage arraysplitting, memory copies, multiple parallel invocations, and passing theloop inputs and iteration schedule to each worker wrapper. Each splitloop may runs over the scheduled iteration block using the given input.The scheduler may wait for all iterations to finish and join/resolve theoutput (e.g., via reduction and/or merge operations).

Thus, in this strategy, the iteration set is split into blocks of citerations to operate on, and each block is queued up in the schedulerqueue. Each of the P workers pulls a block of iterations from the queueand executes those iterations, using the appropriate blocks of the inputarrays and outputting associated results. When a worker finishes itsblock and needs more work, it gets the next block of iterations. Notethat this allocation does not necessarily proceed in round-robin order(as the static schedule does). For example, with 4 workers, if worker 3completes its current block before worker 2, it asks the scheduler forthe next available block instead of just grabbing its staticallypredesignated next block.

Dynamic Decreasing Blocks

In one embodiment of dynamic decreasing blocks scheduling, iterationsmay be divided into increasingly, e.g., exponentially, linearly, etc.,smaller blocks, e.g., where each next block size is equal to the (numberof remaining iterations)/[P], and where P is the number of workers. Thisapproach makes the last blocks smaller to minimize the chance of aworker being assigned a large set of work at the moment when most of theworkers are finished processing. Note that the user does not need tospecify a block size for this schedule. However, if a value isspecified, e.g., by wiring the value to a border node [C], the value maybe used to specify a minimum block size.

Thus, for example, in a dynamic decreasing blocks or guided schedule,which may be denoted Guided(P, C), each thread may be assigned a largeblock or subset (e.g., a multiple of c if wired) on a first pass, and anincreasingly smaller block/subset on each following pass, e.g., down tosome limit of c elements/iterations. The block size may be dynamicallycomputed as needed (usually as N-remaining/T, where N-remaining denotesthe remaining elements/iterations, and T denotes the number of executionthreads). Thus, this approach is similar to the dynamic schedule, butwith a decreasing block size. This type of schedule may be mostappropriate for load-balancing, especially if each iteration can take avariable amount of time. In one embodiment, in both the dynamic andguided scheduling cases, the method may include (a thread process)querying a scheduler to dynamically determine the next subset or blockof iterations to execute, and claiming that subset/block with thescheduler.

User-Specified Partitioning

In one embodiment of a dynamic schedule in which the user specifiespartitioning of the iterations, a user may provide a set of integersspecifying a series of block sizes, e.g., the user may wire an array ofintegers to the [C] border node to specify a series of block sizes. Thisapproach may be useful for experimenting with new (or existing)partitioning/scheduling strategies.

Note, however, that in this approach, cases where the user specifies toofew or too many block sizes may need to be handled. For example, ifthere are too many, the extra block sizes may be ignored. If there aretoo few, the last block size in the array may be used for all remainingblocks (or 1 may be used for all block sizes if the array is empty).Similarly, block sizes less than 1 may be upped to 1.

Another variant of the dynamic scheduling strategy uses dynamicscheduling with dynamic allocation. In this strategy, dynamic allocationis performed based on K (determined at edit or compile time) or a userspecified value T (determined at run-time). In one embodiment, thecorrect number of workers to implement may be determined dynamically (atrun-time).

Note that a static schedule may outperform a dynamic schedule for largenumbers of loop instances, because requesting blocks of iterations maycause a bottleneck. However, a dynamic schedule may outperform a staticschedule when the work cannot be balanced easily.

It should also be noted that for at least some of these schedule types,a processing structure, e.g., an execution thread, can be assignedmultiple (disjoint) subsets of the iterations, i.e., multiple blocksthat may not be contiguous with respect to each other. Note also that inthe dynamic and guided scheduling cases, the method may also includequerying a scheduler to dynamically determine the next subset ofiterations to execute, and claiming that subset with the scheduler.

Summarizing the above: a static block schedule may be appropriate foralgorithms where the work is divided evenly among iterations; a staticblock cyclic schedule may be appropriate for algorithms where some partsof the iteration space contain more work and sampling across theiteration space will balance the work; a dynamic fixed blocks schedulemay be appropriate for algorithms where the work cannot be dividedevenly using a block cyclic partitioning, and the user has found a moreefficient block size than the adaptive partitioning dynamic decreasingblocks provides; a dynamic decreasing blocks schedule may be appropriatefor algorithms where the work may vary across the iteration space, andthe user does not want to take the time to find a good block size; and auser-defined partitioning schedule may be appropriate for algorithmswhere the user wants to provide a specific partitioning, which mayinvolve or require specialized knowledge.

Exemplary Schedule Performance Comparison

As mentioned above, computation of the Mandelbrot set is a good exampleof an application with substantial imbalances in the work performed perpixel/point, and thus, per iteration or iteration block.

FIG. 17 illustrates performance differences between exemplary graphicalprograms for computing the Mandelbrot set according to variousscheduling strategies, specifically, according to a static blockschedule, labeled “Par For”, a static block cyclic schedule, labeled“Block Cyclic”, a dynamic fixed blocks schedule, labeled “Dyn FixedSize”, and a dynamic decreasing blocks schedule, labeled “DynDecreasing”.

As may be seen, FIG. 17 shows how much more effective the static blockcyclic, dynamic fixed blocks, and dynamic decreasing blocks schedulesare than the static block schedule for this type of problem. Note thatthe parallel efficiency for the static block schedule (Par For) dropswith additional worker/loop instances since this strategy is not loadbalancing.

In this example, the dynamic fixed size schedule gives the bestperformance; however, achieving that performance requires selecting thebest block size for each number of worker/loop instances. The dynamicdecreasing schedule also performs well, and it doesn't requireconfiguration by the user (the minimum block size used was 1, which isthe default). The block cyclic schedule also does well, but it doesn'tperform quite as well when there are more than four worker/loopinstances.

Correctness Issues

It should be noted that out-of-order computation may produce differentresults for serial vs. parallel code when using fixed or floating pointoperations, which may have bearing on implementations using programmablehardware elements, e.g., on implementations using field programmablegate arrays (FPGAs).

Auto-Chunking

Array ordering between an input and output array should be maintained.Such ordering may be achieved via “autochunking”, where “chunk” refersto a block of array elements, i.e., an array block, e.g., a “block”.Since the worker rank and the blocksize/schedule are known, where in thelarger array a subArray block should go is also known. It may also bepossible to inplace everything if cache/memory conflicts can be avoided.This knowledge may also be used to build similarly ordered arrays fromassociated scalar outputs from each iteration.

Multiple Auto-chunked Arrays: If two arrays of different sizes are pipedinto a parallel FOR loop, the smaller array may be used to determine theblocksize, and the extra elements of the larger array may be ignored.

Inplaceness: In some embodiments, an attempt may be made to usesubarrays to do all processing in place, if possible. Chunks (arrayblocks) may be aligned to cache line boundaries to reduce cacheconflicts.

Reduction Operation Analysis

Regarding reduction operation analysis, discussed briefly above, in someembodiments, performing reduction operation analysis of the graphicaldata flow program may include automatically detecting reductionoperations, such as, for example, one or more of: add, multiply, min,max, AND, OR, or XOR operations, among others, and analyzing thedetected reduction operations. Note that these operations may be used tocollect and merge results from different iterations or iteration blocks,and thus, for example, may also be appropriate for use in mergingresults from the plurality of second data flow program portions. Furtherexemplary reduction operations may include first, last, build-array,string-concatenation, or error-merge, among others.

In some embodiments, information specifying a merging or reductionoperation for the second data flow program portions may be received, andautomatically generating program code implementing a plurality of seconddata flow program portions may include automatically generating programcode implementing the merging or reduction operation. Execution of theplurality of second data flow program portions may produce a pluralityof result portions, and a merging or reduction operation (possiblygenerated automatically, as noted above) may be executed (as part of thedata flow program execution) to merge the plurality of result portionsinto a merged result.

It should be noted that many, if not most, uses of shift registersresult in cross-iteration dependences that prevent parallelization.However, many associative (but not necessarily commutative) operationsfeeding from a left shift register and feeding into the correspondingright shift register are actually reduction operations. Since the orderof operations is irrelevant, each processing structure may locallyaccumulate its value and the parallel FOR loop can join (i.e., reduce)each of these values into a single scalar using the same reductionoperation. In one embodiment, the following basic reduction operationsmay be supported: add, increment, multiply, max, min, AND, OR, XOR,first, last, build-array, string-concatenation, or error-merge, amongothers.

In one embodiment, the above analyses may be performed by a separatetool, e.g., a standalone software program or tool, that may be used orinvoked by or from within a development environment, or independent fromsuch an environment. The tool may be configured to analyze the data flowprogram and to determine parallelizable loops in the data flow program.Further details regarding embodiments of such a tool are provided below.

There are various ways in which the plurality of second data flowprogram portions may be implemented. For example, in one embodiment,automatically generating program code implementing the plurality ofsecond data flow program portions may include generating the pluralityof second data flow program portions, and generating program code thatis executable to perform index set splitting to partition the iterationsof the first data flow program portion into respective index blocks forrespective execution by the second data flow program portionsconcurrently. The generated program code may also be executable to usethe iteration partitions to divide any input data into respective dataportions for respective use by the second data flow program portions,execute at least a subset of the plurality of second data flow programportions using the respective data portions as input, and merge anyrespective sets of results from execution of the second data flowprogram portions into a merged set of results for further use by thedata flow program. Note that the merged set of results is preferablyfunctionally equivalent to results which would have been produced by thefirst data flow program portion.

Wrappers

The above-described implementation that makes copies of the FOR loop,where each copy performs a distinct subset of the original loopiterations may entail substantial compilation time, since there is morecode to analyze in later compilation stages, and increases the size ofthe generated code. For large numbers of “generated parallel loopinstances”, the compilation time is significant. Additionally, theparallelism is limited to the number of loop copies generated atcompilation time, and so users can not increase the parallelism withoutrecompiling. This may cause users to specify large numbers of “generatedparallel loop instances”, e.g., workers or second data flow programportions; however, having unused loop copies causes unnecessary compileand runtime overhead. Note that even though the extra loop copiesexecute zero iterations, there may still be some overhead from computingthe number of iterations to perform and producing default outputs.

Thus, in some embodiments, automatically generating program codeimplementing a plurality of second data flow program portions maycomprise including a modified version of the first data flow programportion in a wrapper invocable by multiple callers for concurrentexecution, thereby implementing the plurality of second data flowprogram portions, e.g., via reentrant invocation of the same function.The wrapper may be invocable to execute the modified version of thefirst data flow program portion with one or more parameters specifyingthe respective one or more iterations to be executed by the second dataflow program portion. Moreover, to implement the plurality of seconddata flow program portions executing the respective one or moreiterations concurrently, a number of invocations of the wrapper to makefor concurrent execution of the second data flow program portions may bedetermined, the wrapper may be invoked the determined number of timeswith respective values for the one or more parameters to execute therespective one or more iterations concurrently. It should be noted thatin various embodiments, the number of invocations to make may bedetermined at compile time (static) or at runtime (dynamic), as desired.

In another embodiment, automatically generating program codeimplementing a plurality of second data flow program portions mayinclude determining a number of modified versions of the first data flowprogram portion to generate for concurrent execution of the second dataflow program portions, and generating a plurality of modified versionsof the first data flow program portion for concurrent execution based onthe determined number, thereby implementing the plurality of second dataflow program portions, where, as noted above, each second data flowprogram portion may be configured with one or more parameters specifyingthe respective one or more iterations to be executed by the second dataflow program portion. Thus, implementation the plurality of second dataflow program portions executing the respective one or more iterationsconcurrently may include executing the plurality of second data flowprogram portions with respective values for the one or more parametersto execute the respective one or more iterations concurrently.

Thus, with dynamic allocation of instances (refer to this document), thenumber of instances requested at runtime are allocated dynamically,i.e., at runtime. The user is thus no longer required to specify a limiton the amount of parallelism available. This approach may be implementedby asynchronously calling the reentrant wrapper (e.g., subVI) in a loopthat executes P iterations, passing in the appropriate inputs to eachcall to specify which subset of the iterations to execute. The wrappermay then place its results into queues (or some other data structure),and the calling code may reconstruct the results from each wrapper.

FIGS. 18A-18D—Exemplary Wrapper for Static Allocation

FIGS. 18A-18D illustrate use of an exemplary wrapper for implementingstatic allocation of workers, i.e., instances of the second data flowprogram portions. More specifically, these figures are directed to agraphical implementation where the wrapper is a subVI, e.g., a graphicalsubprogram that is callable by a graphical program (VI).

FIG. 18A illustrates an original graphical program (VI) that includes aFOR loop, in this case, a parallel FOR loop, i.e., a FOR loop specifiedfor parallelism. As may be seen, this loop iterates some specifiednumber of times, adding the value of each element from an input array toan initial value of 15, and outputting the sum. As also shown, thenumber of instances or workers to implement may be wired into the [P]border node (described below).

FIG. 18B illustrates exemplary graphical program code for a worker,i.e., a corresponding second data flow program portion, e.g., a sub-FORloop. As FIG. 18B shows, the worker code is similar to the original FORloop, but allows specification of a portion of the iterations toprocess, and generates a partial sum as output, which may then be mergedwith results from other wrapper invocations. Note that SR stands for“shift-register”, where shift registers are denoted in the diagram bythe up down arrow border nodes. When the FOR loop of FIG. 18B iswrapped, e.g., in a subVI, the value 15 will be passed in as the“initial shift-register value” on the first wrapper invocation, and thevalue 0 is passed on subsequent invocations. The shift-register willthen accumulate the value from the array's auto-indexed element eachiteration, producing a sum of all array values (plus the initial value15) once the loop has completed all iterations.

FIG. 18C illustrates a graphical user interface (GUI), specifically, afront panel, for the worker code of FIG. 18B, that includes fields forthe number of iterations, the input array, the initial SR value, and thepartial sum (output). Thus, the input parameters for the worker may bespecified via this GUI, and the output may be displayed. It should benoted, however, that in some embodiments, each worker may not, in fact,have such a GUI.

FIG. 18D illustrates an exemplary implementation of the parallelizedversion of the FOR loop of FIG. 18A using the generated worker code ofFIG. 18B with wrappers (in this case, subVIs). As shown, code to computethe number of iterations and the index offset for each worker maygenerate sub arrays from the input array accordingly, and each sub arraymay be passed as input to a corresponding wrapper that includesrespective worker code (FIG. 18B), where each wrapper is labeled “GENSUBVI”. Note that code is also provided or generated to receive theoutputs from each wrapper and generate the final resulting sum, denoted“Sum”.

Note that while in the example of FIGS. 18A-18D allocation of theinstances is static, in other embodiments, the determination andallocation of the instances may be dynamic, e.g., may be made atruntime.

Index Splitting

In general, automatically generating program code implementing theplurality of second data flow program portions includes generating somesort of infrastructure that facilitates parallel execution of blocks ofiterations, and partitioning these iterations into blocks for suchconcurrent execution. For example in one embodiment, automaticallygenerating program code implementing the plurality of second data flowprogram portions may include applying an index set splitting transform.Such a transform may take a traditional serial for loop and logicallysplit the iterations (index set) into blocks to be scheduled out tomultiple processing elements in parallel. The transform may operate tosafely split auto-indexed input arrays (ideally inplace) and branchinput variables before each of the workers (second data flow programportions), as well as join output arrays, resolve output variables, andcreate a synchronization barrier after the worker loops to ensure thatall iterations complete before moving on. Note that values can be joinedat the end of the loop using a reduction operation (+, −, *, max, min,first, last, err, etc.). Note that the result of a reduction can also bean array or cluster of values. In some embodiments, auto-indexed arrayscan be “auto-chunked” into/out-of the structure, splitting an array intoa block (sub-array) for each block of iterations and merging the blocksin order upon completion.

Note that this transform may be beneficial only for sizable computations(since it must overcome splitting overhead), and may be subject to therequirement that there must be no cross-iteration (loop-carried)dependences. Note further that this transform may only be applied aftera successful dependence analysis, i.e., after the first data flowprogram portion has been shown to be parallelizeable.

Parallel Loop Analyzer

In various embodiments, any of the techniques and functionalitiesdisclosed herein may be implemented as part of a developmentenvironment. However, as mentioned above, in some embodiments, the aboveanalyses (and any other functionalities disclosed herein) may beperformed by a separate tool, e.g., a standalone software program ortool, that may be used or invoked by or from within a developmentenvironment, or independent from such an environment. For example, inone embodiment, the tool may be provided by, or even executed on, aserver. In one embodiment, the tool's functionality may be implementedas an API (application programming interface), which may be utilized orotherwise invoked or called by a GUI, e.g., of the separate tool, or, inother embodiments, of the development environment, or even anotherprogram. More generally, while in some embodiments, the tool may bespecifically directed to analyzing data flow programs to determinewhether they can be parallelized, in various embodiments, the tool maybe further executable to perform any of the various techniques andfunctionalities disclosed herein.

Thus, in one embodiment of the method of FIG. 7, the method may includestoring a data flow program that includes one or more iterative dataflow program portions, and automatically analyzing the data flowprogram, including performing dependence analysis for each of the one ormore iterative data flow program portions, thereby determining whethereach of the one or more iterative data flow program portions isparallelizable. More generally, any of the techniques disclosed hereinregarding analysis or parallelization of the first data flow programportion discussed with respect to FIG. 7 may be applied to each or anyof the one or more iterative data flow program portions.

An indication of each of the one or more iterative data flow programportions that is parallelizable may be stored, where the indications arethen useable to parallelize the data flow program. As noted above, invarious embodiments, the analysis of the data flow program, embodimentsof which are described herein, may be performed by a standalone softwaretool, performed by a development environment, or invoked under adevelopment environment.

An indication of each of the one or more iterative data flow programportions that is parallelizable may be displayed. For example, in oneembodiment, each of the one or more iterative data flow program portionsthat is parallelizable may be displayed. In some embodiments, each ofthe one or more iterative data flow program portions that is notparallelizable may be indicated, e.g., program code that preventsparallelization for each of the one or more iterative data flow programportions that is not parallelizable may be indicated.

As discussed above, in some embodiments, user input modifying at leastone of the iterative data flow program portions may be received, and themodified at least one of the iterative data flow program portions may beanalyzed to determine whether the modified at least one of the iterativedata flow program portions is parallelizable. This process may berepeated until the at least one of the iterative data flow programportions is parallelizable, or until it is decided that parallelizationis not to be attempted.

In one embodiment, the method may include: for each of the one or moreiterative data flow program portions, determining one or more of: anidentifier for each of the one or more iterative data flow programportions, a set of induction variables for each of the one or moreiterative data flow program portions, a range of the induction variablesfor each of the one or more iterative data flow program portions, or anesting level of each of the one or more iterative data flow programportions. Note that, as indicated above, in some embodiments, the dataflow program is or includes a graphical data flow program that includesa plurality of interconnected nodes that visually indicate functionalityof the data flow program. Thus, the one or more iterative data flowprogram portions may be graphical iterative structures or elements,e.g., graphical FOR loops.

As described above with respect to the method of FIG. 7, in someembodiments, the method may include parallelizing the data flow program,including parallelizing each of at least a subset of the one or moreiterative data flow program portions that is parallelizable. Moreover,in some embodiments, parallelizing the data flow program may includegenerating a data flow intermediate representation of the data flowprogram, and parallelizing the data flow intermediate representation ofthe data flow program.

Note that the techniques described herein may not only be applied to asingle data flow program portion, or to a plurality of such programportions, but may also be applied to multiple programs. In other words,in some embodiments, the above storing a data flow program,automatically analyzing, and storing an indication, may be performed foreach of a plurality of data flow programs, e.g., the plurality of dataflow programs may be included in a project or program hierarchy. Themethod may include receiving input indicating the project or programhierarchy, and the performing the storing a data flow program,automatically analyzing, and storing an indication for each of theplurality of data flow programs may be performed in response to theinput indicating the project or program hierarchy.

In some embodiments, various of the techniques or method elementsdisclosed herein may be invoked or performed via a graphical userinterface (GUI), e.g., of the program development environment, or of theseparate tool, mentioned above. The following presents various exemplaryembodiments of such a GUI, and is particularly directed to a user-leveltool that analyzes graphical program, e.g., VIs, to find FOR loops thatcan be safely parallelized. In some embodiments, the tool displays theparallelizable loops to users, allowing them to easily find and enableparallelism on loops. Note that while the embodiments described arepresented in terms of LabVIEW VIs (Virtual Instruments), e.g., LabVIEWgraphical programs, the techniques disclosed are broadly applicable toother types of graphical programs, as well. Note further that theembodiments described and illustrated are exemplary only, and are notintended to limit the GUI or tool to any particular form, function, orappearance.

Simple GUI

FIGS. 19A and 19B illustrate an exemplary simple GUI for specifying ordetermining whether parallelism is to be considered for a graphicalprogram loop. In this embodiment, a user may “right-click” on a FOR loopin a graphical program to invoke a menu whereby the user may specifywhether to enable parallelism for the loop, as indicated in FIG. 19A.

In response to enabling the parallelism for the loop, a FOR loopiteration parallelism configuration dialog may be displayed, whereby theuser may configure the parallelism desired, as indicated by FIG. 19B. Anembodiment of this dialog may allow the user to configure the parallelFOR loop via one or more of the following options:

1) Enable Loop Iteration Parallelism: Specifies that parallelism is tobe applied to the FOR loop, if possible.

2) Parallel Scheduling Strategy: Allows the user to specify a schedulingstrategy, such as blocked, blocked cyclic, dynamic self-scheduled, orguided self-scheduled, among others.

3) Number of Generated Parallel Loop Instances: Specifies the number ofworkers (i.e., processing structures) to allocate at compile time (e.g.,subject to a static upper bound).

More Complex GUIs

In other embodiments, the GUI (tool interface) may be more complex.FIGS. 20A-20G are directed to exemplary GUIs for specifying andcontrolling parallel FOR loops and their analysis. In one embodiment,the tool may be configured to automatically detect FOR loops that can besafely parallelized. For example, the tool may analyze all of the FORloops in a current hierarchy or project to determine which can beparallelized. For each loop in a graphical program, the results windowmay list the FOR loops and indicate whether they are safe to parallelizeand whether the user has already enabled parallelism on the loops.

Double-clicking on a loop in the list may open the graphical program andhighlight the loop. If the loop is parallelizable and the user decidesthat the loop contains enough work to be worth parallelizing, the usermay right-click on the displayed FOR loop and enable iterationparallelism.

In one embodiment, specific functions may be invoked by the user via theGUI. For example, a detector may be invoked from a toolbar (or other GUImeans), where, when launched from the toolbar of a project, the detectormay analyze all of the graphical programs in the project and theirsubprograms. Alternatively, when launched from a graphical program(e.g., VI), the detector may analyze the current graphical program andits subprograms.

FIG. 20A illustrates one embodiment of a GUI whereby the user may invokethe detector. As may be seen, in this exemplary GUI, the invocation maybe made via a “Detect Parallelizable Loops” menu item, which is under a“Performance Analysis” submenu under a more general “Tools” menu on thetoolbar. In one embodiment, when the detector is selected from the menu,a progress window may be displayed showing the percent of graphicalprograms that have been analyzed. The user may stop the analysis fromthe progress window, and the results window may display the informationcollected thus far. When the detector is chosen from a project, theprogress of loading the graphical programs into memory may be displayedfirst. FIG. 20B illustrates one embodiment of such a progress indicator.

When the analysis is complete, a results window may list the FOR loopsthat can safely be parallelized. FIG. 20C illustrates one embodiment ofan exemplary results window that displays FOR loops for each of aplurality of VIs (graphical programs).

In one embodiment, the user may double-click on a FOR loop in the listto open the graphical program and highlight the loop. For example, theuser may right-click on the loop and select “Configure IterationParallelism . . . ” (or equivalent) to enable parallelism. Note thatbecause it may be desirable for users to consider whether each loop isworth parallelizing, in some embodiments, enabling parallelism on loopsmay not be invoked from this window; there is overhead associated withthe parallelism, and on loops with little computation, enablingparallelism can degrade performance. It would be undesirable for usersto enable parallelism on all of their loops at once and then feelcheated if their application slows down.

In one embodiment, the results window may only reflect changes made tothe loops when a “Refresh” button is clicked, which may invoke theanalysis again and repopulate the results window.

In this embodiment, a glyph next to each FOR loop represents whether itis safe to parallelize, where “Safe for parallelism” is represented witha “thumbs up” icon, warnings are represented with a (yellow) cautionsymbol, and errors are represented with an (red) x. If the loop alreadyhas parallelism enabled, there a (green) P is displayed on the glyph.Note that the glyphs shown are exemplary only, and that any otherglyphs, icons, labels, or symbols may be used as desired, e.g.,including, for example, “transparent” icons. Such glyphs may be referredto more generally as parallel FOR loop indicators, and are described inmore detail below.

In this example, the symbol next to the graphical program indicates themost “promising” result of all loops inside the graphical program. Thefollowing is an exemplary order of denotations or parallelizability,ranked from most to least reliable.

1. Safely Parallelizable.

2. Already Parallelized.

3. May Be Safely Parallelizable (has warning).

4. Already Parallelized with Warnings.

5. Not Safely Parallelizable (has errors).

6. Already Parallelized with Errors.

The loops may be listed with their labels. Most loops may have thedefault “For Loop” label. The loops may be labeled (numbered) with thedefault label to help users distinguish the loops (“For Loop #”), butthe numbers may be somewhat arbitrary. It may be confusing to users ifthe numbers/labels changed when the results were refreshed, and so theassigned label may be fixed.

In one embodiment, the results window may display the graphical programname, and a “tip strip” may display the graphical program's full path.In one embodiment, the graphical programs may be primarily sorted bygraphical program name and secondarily sorted by path.

As may be seen in FIG. 20D, a “description” box may be presented (seebottom of GUI) wherein the results for the selected FOR loop may beexplained. The description box may explain how to enable parallelism,state that the loop is already parallelized, or list the potentialerrors and warnings, among other information.

As illustrated in FIG. 20E, in one embodiment, the results window may besimplified by using a list box that the user can sort. The user may beallowed to focus on different types of loops by sorting the results. Inone embodiment, the icons may invert their colors if selected, or onlythe FOR loop column may be shown as selected.

By default, the columns may be sorted by result first, then by graphicalprogram name, and then by whether parallelism has already been enabled.With this sort, users can easily view all of the FOR loops that can beparallelized. If users do not want to look at the loops they havealready parallelized, they may click the top of the “Enabled” column toput the already parallelized loops at the bottom, as illustrated in FIG.20F.

If users want to examine particular graphical programs, they may sort bythe graphical program name primarily (not shown).

As shown in FIG. 20G, a “Test Errors” tab of the results window may listany errors encountered during the analysis (e.g., “not able to load VI”,“the VI is password protected”, etc.). As Figure G also shows, an errordescription box may be provided that explains the errors, e.g., inresponse to user selection of an error. Of course, in other embodiments,errors may be displayed in any manner desired.

In one embodiment, a simple parallel loop detection function (orfunction node) may simply return a list of parallelizable loops. FIG. 21shows an exemplary call to such a function. Note, however, that thissimple function (node) does not support errors or warnings.

In another embodiment, a more complex parallel loop detection function(or function node) may be provided that returns all FOR loops with theirparallelization errors and warning, as illustrated in FIG. 22. Note thatin this exemplary embodiment, the function takes two Booleans as input:a “report conflicts” input that specifies whether the function shouldfind the reasons that a loop cannot be parallelized instead of simplysaying that it cannot; and an “analyze all loops” input that specifieswhether the analysis should visit all loops or just visit the loopswhere parallelism has been enabled by the user. In some embodiments, thetool or GUI may set both inputs to true, e.g., by default.

The output of this more complex function may be an array of clusters. Asindicated in FIG. 23, the output may be presented via an indicator orGUI element that identifies each FOR loop, its conflicts, if any, and/orwhether the loop is safely parallelizable, e.g., via an enum thatcontains “invalid”, “parallelizable”, “has warnings”, and “has errors”.An enum may similarly be defined for conflicts.

In one embodiment, the tool/GUI may provide the following functionality:

A. Preparation for Analysis

-   -   1) Get the paths of all graphical programs in the hierarchy.    -   2) From a project, traverse the list of graphical programs.    -   3) Avoid analyzing a graphical program more than once if it        appears in multiple hierarchies of a project.

B. Analysis Engine (Progress Window)

-   -   1) Collect errors and pass them to the results window.    -   2) If a graphical program is broken, the detector function may        mark all loops it cannot analyze with “has errors”. The results        window may explain in the description box that these loops could        not be analyzed.    -   3) Update the progress window after the analysis of each        graphical program.    -   4) Monitor the Stop button during the analysis.

C. Results Window

-   -   1) Hide the list and show a dummy list while populating the        results. Defer panel updates while the list is populating.    -   2) Store a mapping from item tag in the tree to FOR loop        Reference to know which FOR loop is selected in the list tree.    -   3) Call a helper program to highlight a FOR loop.    -   4) Close references when the window is closed.        Graphical Indicator

As discussed above, in some embodiments, a graphical indicator may beused to indicate whether a specified portion of the graphical data flowprogram, such as the first data flow program portion described above, isto be (attempted to be) parallelized. For example, in some embodimentsof the method described above with respect to FIG. 7, e.g., in which thedata flow program is a graphical data flow program, the graphical dataflow program may be displayed in response to user input, where thegraphical data flow program may include a graphical indicator thatspecifies to a compiler that the compiler is to attempt to automaticallygenerate data flow program code that parallelizes a specified portion ofthe graphical data flow program for concurrent execution, e.g., thefirst portion of the graphical data flow program.

In one embodiment, the specified portion of the graphical data flowprogram is or includes an iterative graphical program element configuredto iteratively execute associated graphical data flow program code,e.g., a FOR loop. For example, the iterative graphical program elementmay be or include a graphical loop structure with an interior, where theassociated data flow program code is contained in the interior of theiterative graphical program element. A FOR loop that includes or iscoupled to such a graphical indicator may be referred to as a parallelFOR loop, because it is slated for parallelization. In some embodiments,the iterative graphical program element, e.g., FOR loop, may include thegraphical indicator. In other words, the graphical indicator may beattached to, or part of, the iterative graphical program element. Forexample, the graphical indicator may be or include a configurablegraphical element on the iterative graphical program element.

Embodiments of such a graphical indicator are illustrated in FIGS. 8A,8B, 15, and 18A, where the indicator is implemented as a “P” border nodeor terminal on the graphical FOR loop in each block diagram. Thegraphical indicator, which may be denoted as [P], may visually show theuser when they (or perhaps the automatic parallelization analysis) haveselected a loop to attempt to parallelize. The dependence/reductionoperation analysis may then be performed at edit-time on all loopsmarked with this indicator, and errors/warnings reported if necessary.In one embodiment, if the analysis passes, e.g., if no errors orwarnings preventing parallelization are discovered, then parallelizationmay proceed. The compiler may then transform any loops marked asparallel (since they must have passed the analysis for compilation to beallowed) and generate the appropriate parallel code, possibly inresponse to user input invoking the compilation.

In various embodiments, the configurable graphical element on theiterative graphical program element may indicate that parallelization isto be attempted via any of various characteristics, e.g., color, shape,or label, among others. Note that in some embodiments, the graphicalindicator may not be displayed (or possibly even included in theprogram) when the loop is not marked for parallelization.

In one embodiment, the graphical indicator may include an appearance ofthe iterative graphical program element that indicates parallelizationof the specified portion of the graphical data flow program is to beattempted. For example, the appearance of the iterative graphicalprogram element that indicates parallelization of the specified portionof the graphical data flow program is to be attempted may include one ormore of: color of the iterative graphical program element, shape of theiterative graphical program element, line style of the iterativegraphical program element, or labeling of the iterative graphicalprogram element, among others. Thus, a user may be able to determinewhether parallelization is to be attempted based solely on theappearance of the graphical loop structure.

As indicated above, in other embodiments, the graphical indicator may beseparate from, but coupled to, the iterative graphical program element.For example, the graphical indicator may be or include a node orterminal that is wired to the iterative graphical program element.

In some embodiments where the graphical indicator is configurable, thegraphical indicator may be configurable to indicate whether or notparallelization of the specified portion of the graphical data flowprogram is to be attempted. Thus, a user (or software) may specifywhether or not parallelization of the specified portion is to beattempted. If the program portion has already been determined to beparallelizable, configuring the indicator to specify thatparallelization is not to be attempted may thus prevent the compilerfrom parallelizing the program portion. If the analysis has not yet beenperformed, configuring the indicator to specify an attempt toparallelize may specify or invoke the analysis to be performed.

The graphical indicator may thus be configured to receive inputspecifying whether or not parallelization is to be attempted, e.g.,input from a user or from an analysis process or tool. Moreover, in someembodiments, an appearance of the graphical indicator may be modified inaccordance with the input. Similarly, in one embodiment, if thespecified portion of the graphical data flow program is determined tonot be parallelizable, the appearance of the graphical indicator may bemodified to indicate that the specified portion of the graphical dataflow program is not parallelizable. In some embodiments, the graphicaldata flow program may be displayed in a graphical program developmentenvironment configured to receive such input specifying whether or notparallelism is to be attempted, and the appearance of the graphicalindicator may be modified in accordance with the input, where, as notedabove, the input may be user input, or may be received from a loopanalyzer tool (whether separate, or included in the developmentenvironment) configured to determine whether or not the specifiedportion of the graphical data flow program is parallelizable.

As mentioned above, if the specified portion of the graphical data flowprogram is determined to not be parallelizable, or a warning conditionis detected, one or more errors regarding why the specified portion ofthe graphical data flow program is not parallelizable, or one or morewarnings regarding parallelization of the specified portion of thegraphical data flow program, may be presented. For example, adescription of the one or more errors or one or more warnings may bedisplayed, offending program code may be highlighted or shaded,suggested modifications to the data flow program may be displayed, orthe appearance of the graphical indicator may be changed. The one ormore errors or one or more warnings may be received from a loop analyzertool in response to the loop analyzer tool analyzing the graphical dataflow program. Various embodiments of such a tool are described above.Note that the generation or display of such errors and warnings may ormay not be associated with the graphical indicator.

Thus, a graphical indicator may be used to indicate and/or specifywhether or not to attempt parallelization of an iterative programelement in a graphical data flow program.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

We claim:
 1. A non-transitory computer accessible memory medium thatstores program instructions executable by a processor to: store a dataflow program, wherein the data flow program comprises one or moreiterative data flow program portions, wherein each iterative data flowprogram portion comprises data flow program code configured to executerepeatedly in an iterative manner; automatically analyze the data flowprogram, including performing dependence analysis for each of the one ormore iterative data flow program portions, thereby determining whethereach of the one or more iterative data flow program portions isparallelizable, wherein said performing dependence analysis comprisesdetermining whether output from a first subset or iteration of data flowprogram code of the iterative data flow program portion is required by asecond subset or iteration of the data flow program code of theiterative data flow program portion; and store an indication of each ofthe one or more iterative data flow program portions that isparallelizable, wherein the indications are useable to parallelize thedata flow program.
 2. The non-transitory computer accessible memorymedium of claim 1, wherein to automatically analyze the data flowprogram, the program instructions are executable to determine that atleast one of the one or more iterative data flow program portions cannotbe parallelized as specified, wherein the program instructions arefurther executable to: indicate one or more errors preventingparallelization or one or more warnings regarding parallelization. 3.The non-transitory computer accessible memory medium of claim 2, whereinto indicate one or more errors preventing parallelization or one or morewarnings regarding parallelization, the program instructions are furtherexecutable to: indicate data flow program code that caused thedetermined errors or warnings.
 4. The non-transitory computer accessiblememory medium of claim 3, wherein the program instructions are furtherexecutable to: receive user input selecting at least one error of theone or more errors or at least one warning of the one or more warnings;wherein the data flow program code is indicated in response to the userinput selecting at least one error of the one or more errors or at leastone warning of the one or more warnings.
 5. The non-transitory computeraccessible memory medium of claim 2, wherein the program instructionsare further executable to: receive user input modifying the data flowprogram code in response to the one or more errors preventingparallelization or one or more warnings regarding parallelization. 6.The non-transitory computer accessible memory medium of claim 1, whereinto automatically analyze the data flow program, the program instructionsare further executable to: automatically determine any side effects ofthe data flow program comprised in the one or more iterative data flowprogram portions.
 7. The non-transitory computer accessible memorymedium of claim 1, wherein to automatically analyze the data flowprogram, the program instructions are executable to automaticallyperform reduction operation analysis of the one or more iterative dataflow program portions.
 8. The non-transitory computer accessible memorymedium of claim 1, wherein to perform dependence analysis, the programinstructions are further executable to: detect cross-iterationdependences that would prevent parallelization.
 9. The non-transitorycomputer accessible memory medium of claim 8, wherein to performdependence analysis, the program instructions are executable to:recognize an early termination condition that prevents parallelization.10. The non-transitory computer accessible memory medium of claim 8,wherein to perform dependence analysis, the program instructions areexecutable to: determine any conflicting array accesses acrossiterations of the one or more iterative data flow program portions. 11.The non-transitory computer accessible memory medium of claim 10,wherein to determine whether there are any conflicting array accessesacross iterations of each of the iterative data flow program portions,the program instructions are executable to: for each of the one or moreiterative data flow program portions: determine an integer linearprogramming problem (ILP) that corresponds to each pair of arrayaccesses in the iterative data flow program portion; and determinewhether there is a feasible solution to each ILP, wherein if there is nofeasible solution to any of the ILPs, then there are no conflictingarray accesses across iterations of the iterative data flow programportion.
 12. The non-transitory computer accessible memory medium ofclaim 10, wherein the data flow program comprises one or more arrayaccess operations, wherein to determine any conflicting array accessesacross iterations of the one or more iterative data flow programportions, the program instructions are further executable to: for eacharray access operation, determine a source set of operations, comprisingthe set of operations that define some or all input values for the arrayaccess operation; and determine a destination set of operations,comprising the set of operations that use some or all output values ofthe array access operation; wherein to automatically analyze the dataflow program, the program instructions are further executable to:analyze each of the one or more array access operations, including thesource set of operations and the destination set of operations for eacharray access operation.
 13. The non-transitory computer accessiblememory medium of claim 12, wherein to automatically analyze the dataflow program, the program instructions are further executable to: foreach array access operation, determine a list of one or more readexpressions representing a set of array elements from which the arrayaccess operation may read; and determine a list of one or more writeexpressions representing a set of array elements to which the arrayaccess operation may write; wherein to automatically analyze the dataflow program, the program instructions are further executable to:analyze each of the one or more array access operations, including theone or more read expressions and the one or more write expressions foreach array access operation.
 14. The non-transitory computer accessiblememory medium of claim 1, wherein to automatically analyze the data flowprogram, the program instructions are further executable to: generate adata flow intermediate representation of the data flow program; andanalyze the data flow intermediate representation.
 15. Thenon-transitory computer accessible memory medium of claim 1, wherein theprogram instructions are further executable to: parallelize the dataflow program, including parallelizing each of at least a subset of theone or more iterative data flow program portions that is parallelizable.16. The non-transitory computer accessible memory medium of claim 15,wherein to parallelize the data flow program, the program instructionsare further executable to: generate a data flow intermediaterepresentation of the data flow program; and parallelize the data flowintermediate representation of the data flow program.
 17. Thenon-transitory computer accessible memory medium of claim 1, wherein theautomatic analysis of the data flow program is performed by a standalonesoftware tool.
 18. The computer accessible memory medium of claim 1,wherein the automatic analysis of the data flow program is performed bya development environment.
 19. The non-transitory computer accessiblememory medium of claim 1, wherein the automatic analysis of the dataflow program is invoked under a development environment.
 20. Thenon-transitory computer accessible memory medium of claim 1, wherein theprogram instructions are further executable to: display an indication ofeach of the one or more iterative data flow program portions that isparallelizable.
 21. The non-transitory computer accessible memory mediumof claim 20, wherein to display an indication of each of the one or moreiterative data flow program portions that is parallelizable, the programinstructions are further executable to: display each of the one or moreiterative data flow program portions that is parallelizable.
 22. Thenon-transitory computer accessible memory medium of claim 1, wherein theprogram instructions are further executable to: indicate each of the oneor more iterative data flow program portions that is not parallelizable.23. The non-transitory The computer accessible memory medium of claim22, wherein to indicate each of the one or more iterative data flowprogram portions that is not parallelizable, the program instructionsare further executable to: indicate program code that preventsparallelization for each of the one or more iterative data flow programportions that is not parallelizable.
 24. The non-transitory computeraccessible e memory medium of claim 1, wherein the program instructionsare further executable to: receive user input modifying at least one ofthe iterative data flow program portions; and analyze the modified atleast one of the iterative data flow program portions to determinewhether the modified at least one of the iterative data flow programportions is parallelizable.
 25. The non-transitory computer accessiblememory medium of claim 1, wherein the program instructions are furtherexecutable to: for each of the one or more iterative data flow programportions, determine one or more of: an identifier for each of the one ormore iterative data flow program portions; a set of induction variablesfor each of the one or more iterative data flow program portions; arange of the induction variables for each of the one or more iterativedata flow program portions; or a nesting level of each of the one ormore iterative data flow program portions.
 26. The non-transitorycomputer accessible memory medium of claim 1, wherein the data flowprogram comprises a graphical data flow program comprising a pluralityof interconnected nodes that visually indicate functionality of the dataflow program.
 27. The non-transitory computer accessible memory mediumof claim 1, wherein the program instructions are further executable to:perform said storing a data flow program, said automatically analyzing,and said storing an indication for each of a plurality of data flowprograms.
 28. The non-transitory computer accessible memory medium ofclaim 27, wherein the plurality of data flow programs are comprised in aproject, wherein the program instructions are further executable to:receive input indicating the project; wherein said performing saidstoring a data flow program, said automatically analyzing, and saidstoring an indication for each of the plurality of data flow programs isperformed in response to the input indicating the project.
 29. Thenon-transitory computer accessible memory medium of claim 27, whereinthe plurality of data flow programs are comprised in program hierarchy,wherein the program instructions are further executable to: receiveinput indicating the program hierarchy; wherein said performing saidstoring a data flow program, said automatically analyzing, and saidstoring an indication for each of the plurality of data flow programs isperformed in response to the input indicating the program hierarchy. 30.A computer implemented method, comprising utilizing a computer toperform: storing a data flow program, wherein the data flow programcomprises one or more iterative data flow program portions, wherein eachiterative data flow program portion comprises data flow program codeconfigured to execute repeatedly in an iterative manner; automaticallyanalyzing the data flow program, including performing dependenceanalysis for each of the one or more iterative data flow programportions, thereby determining whether each of the one or more iterativedata flow program portions is parallelizable, wherein said performingdependence analysis comprises determining whether output from a firstsubset or iteration of data flow program code of the iterative data flowprogram portion is required by a second subset or iteration of the dataflow program code of the iterative data flow program portion; andstoring an indication of each of the one or more iterative data flowprogram portions that is parallelizable, wherein the indications areuseable to parallelize the data flow program.
 31. The method of claim30, wherein said automatically analyzing the data flow program comprisesdetermining that at least one of the one or more iterative data flowprogram portions cannot be parallelized as specified, the method furthercomprising: indicating one or more errors preventing parallelization orone or more warnings regarding parallelization.
 32. The method of claim31, wherein said indicating one or more errors preventingparallelization or one or more warnings regarding parallelizationcomprises: indicating data flow program code that caused the determinederrors or warnings.
 33. The method of claim 32, further comprising:receiving user input selecting at least one error of the one or moreerrors or at least one warning of the one or more warnings; wherein thedata flow program code is indicated in response to the user inputselecting at least one error of the one or more errors or at least onewarning of the one or more warnings.
 34. The method of claim 30, whereinsaid performing dependence analysis comprises: determining anyconflicting array accesses across iterations of the one or moreiterative data flow program portions.
 35. The method of claim 34,wherein said determining any conflicting array accesses acrossiterations of each of the iterative data flow program portionscomprises: for each of the one or more iterative data flow programportions: determining an integer linear programming problem (ILP) thatcorresponds to each pair of array accesses in the iterative data flowprogram portion; and determining whether there is a feasible solution toeach ILP, wherein if there is no feasible solution to any of the ILPs,then there are no conflicting array accesses across iterations of theiterative data flow program portion.
 36. A system, comprising: means forstoring a data flow program, wherein the data flow program comprises oneor more iterative data flow program portions, wherein each iterativedata flow program portion comprises data flow program code configured toexecute repeatedly in an iterative manner; means for automaticallyanalyzing the data flow program, including performing dependenceanalysis for each of the one or more iterative data flow programportions, thereby determining whether each of the one or more iterativedata flow program portions is parallelizable, wherein said performingdependence analysis comprises determining whether output from a firstsubset or iteration of data flow program code of the iterative data flowprogram portion is required by a second subset or iteration of the dataflow program code of the iterative data flow program portion; and meansfor storing an indication of each of the one or more iterative data flowprogram portions that is parallelizable, wherein the indications areuseable to parallelize the data flow program.